The Wii U isn't likely to be the lead platform anytime soon for any 3rd multi-platform party title, just like the PS3 wasn't the lead platform on 360/PS3 titles most of the time except for a handful of multi-platform titles. The lead platform tends to be either whatever the developer is most comfortable working on or the one that will likely have the most sales. This generation, that was the Xbox 360. When the Wii U releases, the lead platform will likely remain the 360 until Microsoft and Sony's new consoles release, especially because it's so relatively easy to simply up the texture resolution and whatnot for the Wii U version while keeping the lower spec-ed 360 and PS3 as the baseline. Then the lead platform will shift to whatever new platform meets the criteria I've already listed.
Digital download titles would be a different story, but the only way the Wii U would be a "lead platform" there would be if they were timed exclusives or were designed to use the Wii U tablet's unique features.