Initially while companies are working on PS3/Xbox and PS4/Xbox720 versions I think it will be less of a problem, but as the PS3/Xbox games get less and less, I feel the Wii-U will then get less (i.e it will get games where there is an equivalent last gen game being made).
Of course, there is one big issue here, and that is the cost of maintaining so many different versions of the same game, So lets think for a moment that companies will be making a multi gen game, they would need engines/people to support:
PS4, Xbox720, Ps3, Xbox360, PC and Wii-u... this is starting to get a bit ridiculous, and they may end up missing the wii-u out... if any initial games sell badly... or if the console doesn't look like its going to get the gamers that will buy those types of games. We've already seen this with certain engines (Unreal) and certain games not coming out on the Wii-u already...
This was always going to be the problem with the wii-u and the low end specs they decided to launch with... Nintendo really imho need to start spending the cash on 2nd party games etc... but that takes time, and by the time it actually happens will it be too late. Going to be an interesting year or two.