Eusis already touched on this point, but almost all the "Mature" games that didin't do well ont he Wii wouldn't have done any better on the 360 or PS3.
Meanwhile, the Wii has several "Hardcore" games that have hit over a million, including RE4, at least two of the Medal of Honor games, and a few others I can't think of off the top of my head.
But that said, you also have to understand that Wii games COST a lot less to produce in general, so they don't need to push a million to make a profit. While a PS3 game might cost several million to make and require 1.5 million sales just to break even, several Wii games start making a profit around the 200k mark. Like, for instance, Umbrella Chronicles, which didn't hit a million but still made a tidy enough profit for Capcom to want to make Darkside Chronicles, which itself made a handsome profit despite never hitting a million.
The Wii is a completely different business from the 360 and the PS3, and thinking in the same terms as on thsoe systems makes for a lot of faulty assumptions.