Before any of you go "That's ridiculous! It's in the name!" no game will require it, due to the slider, so it's not going to be vital for any game.
The big reason is that it would offer a lower price model down the line in the event that sales after the launch don't keep up, the way that the PSP and PS3 prices hurt their sales being too high for the market used to lower prices for handhelds and home systems.
Yes, this means I think the price is too high for the system. Not a hell of a lot too high, but too high nonetheless. I know Nintendo has dreampt of 3D since the Virtual Boy failed, but aside from the possibility of adding depth perception, it doesn't actually improve the games themselves, same as 3D in movies (save possibly for Avatar) and HD for movies and TV shows (sports are an exception, since you can't stage them to make everything visible).
This seems to be more about the obsession the gaming industry has with making gamers forget they are playing a game, without considering that might NOT be what the mainstream wants. We want better games, not games that try to pretend they are something else (as in the former is the reason games sell, while the latter seems to be what gets good reviews). Here, the cost is too high, while the content gain is too little to make up for it.
A flashy-first game is awesome when it comes out. A great-first game is awesome forever.
Plus, just for the hell of it: Kelly Brook at the 2008 BAFTAs