The platform holders wants the best that third party publishers have to offer.
If you've ever despaired at the online provisions available on the Wii, rest assured that things will be very different with the Wii U. Very, very different in fact, as Nintendo is apparently more than happy for third party publishers to use their own networks on the Wii U.
Nintendo of America president Reggie Fils-Aime says that Nintendo had decided to sidestep the arguments with publishers over using their own systems. He said that Nintendo wanted to get the best of what the third party publishers had to offer to make. This would mean that deals like the one that Sony reached with Valve over having Steam on the PS3 would be fairly commonplace, and might even open the door to cross-platform play as with the PC and PS3 versions of Portal 2.
This move from Nintendo offers all kinds of potential for other games as well. For example, one of the reasons that Final Fantasy XIV didn't make it to the Xbox 360 was because was because Square Enix wanted to use Xbox Live in a way that Microsoft didn't like. That wouldn't be an issue on the Wii U though, as Square Enix could do whatever it wanted/needed. Obviously, FF XIV didn't turn out to be the best game in the world, so Microsoft probably isn't all that upset it missed out, but the principle remains the same.
What's not clear though, it how the whole system is going to fit together. Nintendo has promised an experience much closer to Xbox Live for the Wii U, but from what Fils-Aime is saying, it sounds like it's going to be much a rather fragmented service, with publishers doing most of the work themselves. Of course, with such a long time until the Wii U actually comes out, this information is incomplete. Nintendo will still need a provision for first part content, and it will be interesting to see what that will be.