If you look at the userbase of this past generation, many Wii gamers bought a PS3 or X360. If they come back to Wii U in full force, you have people who have been exposed to core gamers through a few years.
It`s not a concrete market, but sure is a potential market.
I think the reason you aren`t seeing it right now it`s because Wii U has virtually nothing to offer to the good old Nintendo fan. The only big game is NSMB U, but the same type of look for the fourth time, coming right after NSMB 2, just was a bad choice/decision and has taken it`s toll on Wii U.
With WW, Mario 3D, Yoshi, Pikmin 3 and Mario Kart coming, Wii U`s userbase will grow rapidly and these PS3/X360 owners, if given the chance of buying their favourite 3rd party games on Wii U, will now have a reason to think twice on buying 3rd party games on X720/X360 or PS3/PS4.
