I don't think that source is accurate, but I don't see it as a big deal either.
Black Ops 2 and Assassin's Creed 3 are the biggest third party releases of 2012 and both are on Wii U.
Grand Theft Auto V wouldn't be a shock. It's an easy 1 million (WW shipped) for Rockstar to cash in on, and on these mega-budget titles, every million counts.
Nintendo themselves is setting the pace that the Wii U is not just for family-friendly content with Ninja Gaiden 3 and Bayonetta 2 published by them in-house, third parties shouldn't feel like there has to be certain types of content that can't be on Wii U.
Fact is if Wii 1 could've ran GTAIV without huge compromises, it probably would've gotten a version.