I can expect decent sales, because there is little to nothing else for the consoles consumer at the table. Eventually if a gamer has any lust for mature or complex content they will have to make the choice of which is the lesser of two evils. Resident Evil might be a fine port. However for probably being the best mature game on the console the sales are actually pretty flat. Match it against a Mario Party, or a Paper Mario.
I would call Madden mature compared to the other offerings on the console. I would also point out that Madden seems to sell regardless of quality. Usually a guaranteed million seller on a console. Except on the Wii console last years offering did not even break four hundred thousand. That and it arrived with a holiday console launch. I did not expect this game to do well, but it is looking on track to under perform last years Madden.
I suppose we will find out how anorexic the Wii community is when Metroid makes the scene. However for a Madden to perform this poorly has to give everyone a moment of pause. Less then one in a hundred North American Wii owners bought this game in its first week. That is insanely pathetic.