If Legends was released around now, I think a lot of Wii U owners would have picked it up due to the relative game drought on the console as of now. Now though, more people will pick up Wind Waker HD, Mario Kart U, Wonderful 101 - leaving Rayman Legends on the Wii U platform with less than desirable sales.
You'll have the same situation on the PS3/360, with a lot of AAA titles probably stealing the intended consumer's mind share.
I'll still pick up Rayman Legends, but probably only once I've finished the AAA Nintendo games coming out Q4 - so sometime after Legends has hit the bargain bins.