I think they're thinking that gritty, realistic sports sims haven't done well on the Wii in any region, and they'd be right.
That could change, obviously, but I bet they'd been working their butts off to get a Wii version out if Madden Wii had sold better.
http://i14.photobucket.com/albums/a324/Arkives/Disccopy.jpg%5B/IMG%5D">http://i14.photobucket.com/albums/a324/Arkives/Disccopy.jpg%5B/IMG%5D">