Romantic comedy is an attractive genre for Hollywood: often big bucks at the box office, for lower-than-average production budget (less need for digitally enhanced aliens - plastic surgeries provided by actors themselves). In short, something to get the producers squealing with delight. Traditional Hollywood thinking suggests that marrying romance and comedy creates a match made in date movie heaven, if the romance ropes in the females, and comedy the males. Whether this ploy works in reality or not, the genre's escapist aspect of light-hearted plots and practically guaranteed happy endings appeals to a large chunk of people.
The first romantic comedies date to the infancy of cinema. Le Baromètre De La Fidélité (1909) might be the first rom-com; City Lights is one of the most famous silent era rom-coms. In the 30's-50's romantic comedies (e.g. It Happened One Night, Bringing Up Baby, Some Like It Hot) romantic entanglements and the comedy aspect were equally prominent, with quickfire dialogue and screwball comedy elements. The 60's romantic comedies snuck in more direct sexual references, and also some more cynical undercurrents (e.g. Pillow Talk, The Apartment, Breakfast at Tiffany's). 70's paved way for the "radical romantic comedy", which inspected the ideology of romance, and therefore didn't guarantee a happy ending for the couple (e.g. Annie Hall, Manhattan). The '80s romantic comedies often put comedy first, and employed established comedians (e.g. Tootsie, Coming to America, Roxanne, When Harry Met Sally...).
At the turn of 80's and 90's the critical and commercial success of When Harry Met Sally... and Pretty Woman induced a large-scale resurgence for romantic comedies. Casting Tom Hanks, Meg Ryan, Sandra Bullock, Hugh Grant and/or Julia Roberts seemed to be quickhand for ka-ching. But, the execs seemed to forget that these films worked because they also featured original premises and thoughtful plotting (e.g. While You Were Sleeping, My Best Friend's Wedding, Four Weddings and a Funeral, Sense and Sensibility). The mainstream's increasing reliance on story contrivances has resulted in giving the whole genre a stamp of convention-obsessive disorder.
Industry continued to believe that the right name above the title would guarantee a hit even without an original script. But, the transition from the Hollywood-aging stars to younger, pretty, blonde girls like Cameron Diaz, Reese Witherspoon, Kate Hudson, Jennifer Aniston and Katherine Heigl has proved only unreliably bankable. Rom-com seems to be at crossroads.
The busiest rom-com stars have shared many factors: they're slim, Caucasian, conventionally good-looking people, in their 20's-40s, playing straight roles. This could change, as some of the biggest commercial successes of 00's and 10's have deviated from the previous norm: Hitch and Think Like a Man featured African-American leads. The Best Exotic Marigold Hotel stars love-lorn retirees, and in Hope Springs sixty-somethings Tommy Lee Jones and Meryl Streep get frisky.
In the outskirts of Hollywood, indies and smaller films can approach the genre in a roundabout way, toying with the traditional story arc of Meet Cute - Third Act Trouble - Together-Forever Promise (e.g. About a Boy, The Five-Year Engagement, (500) Days of Summer,Lars and the Real Girl).
Moreover, many newer rom-coms have tickled the moulds by taking cues from the raunchier gross-out films: in Knocked Up woman meets a drunken hook-up; in Forgetting Sarah Marshall man meets ex and Russell Brand; in Bridesmaids Chick Flick conventions meet explosive diarrhea; in The 40-Year-Old Virgin man meets...nothing, for a few decades.
The romance/comedy premise lends itself well for genre couplings, which also handily broadens the potential fanbase. Sometimes the writers add some Speculative Fiction elements to the mix. The woman might be an alien; the man might get a superpower. In Splash the love interest is a mermaid, in Ruby Sparks she's a creation of his mind. Happy Accidents and Safety Not Guaranteed throw (potential) time-travel into the potluck. Most often, this merely produces hilarious complications, but it can also lead to a case of Everything but the Girl.
The writer can additionally dip into sports' movies (e.g. Jerry Maguire), or an adventure flick (e.g. The Princess Bride, Romancing the Stone). Maybe the romance-comedy could menage-à-trois with a historical film (e.g.Shakespeare in Love), a black comedy (e.g. Harold and Maude), or fantasy (e.g. Groundhog Day, L.A. Story).