It seems a lot of people here ( especially Guild ) have a short memory when it comes to consoles launches.
The Wii, for example , in 2006/2007 had quite a few games ported over from PS2 or Xbox with the excuse of new control system or wide screen support. And it worked quite well from developers as well.
The Godfather for example, was skipped on the GC but came out for Wii with improved ( really ) controls, and so did Scarface, Rygar, Bully, and even RE4 ( which was already on GC ) was successfully ported to the WII ( along with most RE games ).
Metroid Prime Trilogy was an exclusive GC, but that didn't stop Nintendo from porting/re-releasing that on the Wii in the name of new play style.
They all had moderately success, and certainly was a quick way to do some cash.
The Wii U has a new, innovative controller, and full HD graphic, what makes you think developers wouldn't want to do the same on the new platform ??
And as aforementioned, the Wii U will get sequels to current gen games that never came out on the Wii, like Assassin Creed, Batman and so on.
It makes only perfect sense that they will port previous installments of those games to the Wii U , and don't forget that HD remakes are very common these days ( God Of war trilogy for PS3, Halo for Xbox 360, Metal gear etc... ) and they only offer HD graphic and compared to last gen.
Of course we will get older games ported to the Wii U , and I'll be very interested if I could get an Assassin Creed trilogy or Bioshock collection on my Wii U.
Some people prefer to have only one console around for their gaming needs you know, not everybody has the space/possibility to own multiple consoles.