I've just posted this response to the question of "Similar but Different" over at one of my favorite screenwriting blogs Go Into the Story, but it's something I'd been meaning to write about for a while so it merits an airing here too:
Everything is a remix. It's much quicker and easier to hook an audience (and therefore much easier to make money) if you can grab them with something they already know they like. You may only have 3 minutes in a trailer, or 30 seconds in a TV ad to tell people about your particular film, but the reason "Similar but Different" works is because if your film looks like 2,000 other films they've enjoyed (and especially if yours has a novel twist) then you've pretty much just bought yourself a quarter million hours advertising per person.
"Similar but Different" has different rules in the UK and Europe than in the US (because our previous cultural output breaks down along very different genre lines) but I'd say we're all still pretty much locked into it whether we know it or not (as are the execs with the money) so I very much doubt that it's ever going away.
Existing properties such as TV shows and previous films will also tap into this, but I doubt it's going to replace original "Genre classic with a twist" or "Genre vs Genre" for long because one specific show can't compete with the entire cultural sensibility and multiple thousands of hours of recognition that an established and well-loved genre can.
The trick is figuring out what to keep the same and what to "twist" - and those rules are different from place to place and keep changing from year to year. The answer, perhaps, is not to skate to where the puck is, but to hit it where you'd like it to go.
What are your thoughts on "Similar but Different" in different cultures and how it changes over time?