I do agree that right before Christmas would sell a lot, but I also know that a lot of people might still want an Xbox 360 or PS3. So an April or May release gives them a good head start. Plus, if they do want to change anything before Christmas sales, releasing it in April gives them more time to adjust things and release more games in time for the holiday season. Having more games available besides the launch titles may do them good.
Edit* Plus, if Microsoft announces something about the next Xbox at E3 2012, alot of people may just skip purchasing the Wii U and wait for the next Xbox. So again, an early launch, in my opinion, is good. I doubt that Microsoft or Sony would announce a new console anyway, but if they announce a whole bunch of games that people want, the people who don't own a console may buy one of the two, and others may just save up for the games and not care for the Wii U. Everyone who does really want a Wii U may buy it regardless, but if Nintendo wants the rest of the people as well, an early launch is good. :3 Okay, I'm going to be quiet now because I feel that I'm repeating myself and I am starting to confuse myself as to which side I'm on. x)
I know a lot of people who are excited for Minecraft on the 360. I know one person who even told me they would sell their PS3 just to buy an Xbox360 to play it. So, I think that would be great if it came to the Wii U.