Defied with EVE, voiced by Elissa Knight. The original intention was to use her voice as a placeholder and hire someone more known later, but they loved her performance too much to replace it (and who could blame them?).
Moe Anthropomorphism: Nearly every robot in the movie has a piece of humanization fanart lurking on deviantArt somewhere. M-O, whose name should already be a direct indication about this. Andrew Stanton even admitted that they "turned up the cute dial too much" with this character.
Revised Ending: Originally, after EVE finished repairing and recharging WALL•E, he expressed confusion at the giant hole in the truck's roof, only for EVE to calm him down by holding his hand. The sequence of WALL•E losing his memory until EVE kisses him was added to give the movie's final scene a stronger emotional punch.
Spell My Name with an S: How many different ways can you write "Buy n Large"? According to the Pixar Wiki, the former is correct. It was "Buy n' Large" shortly after the merging, but it lost its apostrophe with time; shortened to BnL. However, just on this Wiki, you'll find:
According to the commentary, it was originally planned to avert Eternal English (it is 700 years into the future) and have the humans on the Axiom speak a language altered to the point of being unintelligible to viewers. Basically, the sounds-as-dialogue-replacement would have been through the whole movie.
On that note, when WALL•E's body falls out of the Holo-Detector, the original plan was that he'd be leaking oil, and if the storyboards are any indication, he'd eventually be lying in a small pool of it. This detail is present in the junior novelizations, storyboards, and scripts. It's likely it was removed because it looked a littletoomuch likesomething else.
The humans were once green alien blobs. Stanton and the staff did not find them very identifiable and they evolved into globby humans. By the final product, the humans were evolved into the more into baby-types. Also, the Axiom was a fleet of ships that could attach/detach.
Auto was once a typical moving droid rather than the steering wheel of the ship.