I meant NoA when I said they were favoring Mario. I should have been more specific.
WW sold ridiculously well in America. A lot of people know about the other titles. Mario games just sell the best, and the slow start of the 3DS seems to have made NoA too nervous to take a chance ion any IP except Kid Icarus. NoA has only been releasing games that sell the best, not any games that just sell well. (Aka, Mario versus non-Mario.)
I don't think it has anything to do with when AC:3DS will sell best. I think they'll release it during a time when they have low games sales because they think it won't do as well as Mario in the States. I think the best release times are reserved for Mario games. (For example, Paper Mario being release soon, during the holidays, instead of Animal Crossing.)
And again, I don't think the Wii U is a big factor. Otherwise they wouldn't be releasing Paper Mario either. It's simply a matter of 'Paper Mario is filling the Holiday Nintendo 3DS big game slot,' because it will sell better because it's Mario.