You're both missing the point here. It doesn't matter if the Wii U is family friendly or not, why can't TT just put their game on PS3/Xbox 360 as well?
Oh I think I could answer that.
Lego City is perhaps the only recent lego game that isn't based off a stuffty movie tie in. As it is the first and only non-movie based lego game made by TT. They probably needed extra money to fund the project since they were trying to do something slightly original for once. So Nintendo decided to publish it because the wii-u desperately needs games and TT needs money on a non-movie based project.
I assume TT was like "damn we don't have a movie tie in to generate us money, we need to ask someone who desperately needs games to throw us some starting money!"