Adaptation Displacement: The original novel had Joanna only suspecting that the men had replaced their wives with robots. The film went ahead and confirmed it, and these days everyone associates the Stepford Wives with robots.
The original film leaves it open just how much Walter knew about Stepford before he arrived, or how okay he was with the whole process. A line about Carol when they first arrives "I hope she cooks as good as she looks" could be just friendly banter or it could mean that he already knew. Given the scene where Joanna finds him drinking after a meeting, it's possible he didn't know the process involved murdering his wife to begin with.
Charmaine alludes to only playing tennis with teenage boys who fancy her. Given how she's sure that Ed doesn't love her, is she having affairs with these boys on the side?
Broken Base: The wives' outfits. In the original treatment, they were to be dressed "like Playboy bunnies, sans ears". When Nanette Newman was cast, the costumes instead became more like traditional 1950s housewives dresses. The original screenwriter disowned this, citing it unrealistic that men wanting to create sexbots wouldn't make them as sexy as possible. Others however feel that the 1950s dresses emphasise the Stay in the Kitchen satire more than the skimpy outfits would. The remake offers a compromise and puts the wives in flattering sun dresses.
It Was His Sled: The Robotic Reveal of the original was the film's shocking surprise ending. Thirty years later, when the phrase "Stepford Wife" had entered the lexicon, the remake assumed audience familiarity with the concept and played it for laughs.
The social satire here is pretty blatant with the men replacing their liberated feminist wives with submissive domestic robots - but it served to show audiences that forcing women into these domestic roles is damaging and that the wives are people with their own hopes and ambitions too. There's a scene where Walter is in over his head trying to entertain the children, to which Joanna snarks "I've been entertaining them for seven years."
At the time a lot of people thought that it was best to stay in an unhappy marriage rather than subject the children to the unpleasant process of a divorce. The film challenges that idea and shows how unhappy Joanna is in her situation, that she's never treated like an equal in the marriage. Walter is willing to outright kill his wife and have her replaced with a submissive robot to uphold the image of a perfect family. Unsurprisingly the public view changed in favor of divorce rather than Awful Wedded Life by the end of the decade.
Charmaine being a trophy wife is harder to accept these days. By the time of the 80s and 90s, there were far more women in the work force, and Charmaine would have likely had a job before she married Ed. If the film is set at the same year it was released (1975) then Charmaine would have been the right age to have grown up in a conservative household - hence her status as a trophy wife.
Likewise the amount of clashes between Walter and Joanna's preferred choice of lifestyle makes it seem odd to younger viewers why they don't just get a divorce. Bobbie and Charmaine don't appear to be happy in their marriages either. Before 1969 couples had to come up with some form of wrongdoing in the marriage in order to legally justify a divorce, and doing the math with the children's ages would put the Eberharts' marriage as before the no-fault divorce bill was passednote Joanna has a line where she says "I've been entertaining them for seven years", which means the Eberharts have been married since at least 1968. And around the time the book was published, it was still thought better to stay together for the sake of the children even if the parents couldn't stand each other. It was over the next decade that this kind of thinking slowly gave way to more liberal views.
The idea that moving to the suburbs to raise the children was inherently better is also fast dying out. The youth of the 2000s flock towards cities and urban settings, and the old romantic view of peaceful suburban life has been challenged in multiple works like American Beauty, Desperate Housewives, The Ice Storm etc.
Values Resonance: The themes of conforming to traditional gender roles while also trying to be a good wife and mother - and examination of exactly what that involves - are still pretty resonant today.
Vindicated by History: The film was only a modest success at the time, but it has grown in popularity over the years. 'Stepford Wife' has entered the lexicon as an expression, and it spawned several sequels, re-tellings and remakes.
The Woobie: Charmaine is probably the biggest Woobie among the wives. Walter and Joanna seem to have some happy moments, and they've got children they both love. Bobbie and Dave too seem to have a somewhat happy marriage. Charmaine meanwhile was a trophy wife, is fully aware of it and appears to be the loneliest of the women. She's cynically aware that Ed never loved her and the only value she has is based off her looks. If she's the same age as her actress Tina Louise (41 at the time of filming) she's also bound to be anxious that her looks might start to fade soon.
The scene where the husbands use one of the wives as an ATM.
There's also the unstoppable twirling scene and the remote control breast size scene. These were actually meant to be rather blatant Foreshadowing, but were rendered bizarre because of the last minute change to the ending.
While a lot of critics slated the film for taking a comedic approach to the storyline rather than the more serious tone of the previous adaptation, the original novel actually was more comedic in tone than the 1975 film. In fact, that film was actually supposed to be as comedic as this one, but director Bryan Forbes rewrote it and eliminated most of the humor.
The twist of the wives merely being lobotomized, rather than murdered and replaced with lookalike robots, might have came from the sequel films, which also performed this retcon so that the victims could be saved in the end.
Shocking Swerve: The 2004 remake ends with a twist: the wives simply have chips in their brains that are easily deactivated, rather than being robot doubles, so we can have a happy ending. This creates a large plot hole, as it contradicts a few scenes like one of the wives acting like an ATM and spewing dollar bills from her mouth, or the Camp Gay guy apparently looking at his robot double in horror. One deleted scene with Bette Midler's character going nuts with various housecleaning accessories in her body makes it very clear that they were originally intended to be robots. This could be due to the film's multiple reshoots.
What An Idiot: As The Blockbuster Buster pointed out, the husbands should've been put in jail for what they did to their wives...instead their punishment is house arrest and having to perform regular chores performed by the Stepford Wives and are still married to their wives...whom they've tried to brainwash and enslave their wives.
Blockbuster Buster: It's funny because they should be in jail, for consenting to the illegal performance of brain surgery on their wives as well as enslaving them but instead their punishment is to perform everyday common chores for their families.
Though it may have been part of a plea deal with the authorities. Those same husbands were privy to advanced technology in various fields including robotics, cybernetics and neurosurgery. That would benefit humanity greatly and would definitely be worth a reduced sentence or special conditions.
Whether they are still married is questionable. They may be husbands in name only as their wives have very solid (and favorable) grounds for divorce. Plus, we only see one scene of the husbands during their house arrest and they're clearly under surveillance. Finally, we don't see all the husbands; some of them may actually be in prison.