The problem comes in with the fact that Nintendo just chose the specific cutoff of 8.5 rating or higher to support their claim. Is there really a big difference between 8.4 and 8.5? Yet another aspect that has to be taken into account is that the WII U is a year older than the PS4 and Xbox One, as well as the fact that Nintendo games tend to cater do a completely different audience.
While the choice for games scoring an 8.5 or higher is a bit arbitrary, the thing about the Wii U being a year older is just bytching because it's about what's available for the console at the moment you're thinking of buying one. If you're going to buy a console now, Nintendo's right for pointing out they have more acclaimed games than the competition, even if it's through the advantage of being out longer.
And that shyt about Nintendo games catering to a completely different audience is bullshyt as well, unless they mean that Nintendo caters to audiences who love great video games instead of aiming games at gullible fools who pay for unfinished broken games that deliberately withhold elements so they can be sold at a later time as 'DLC'.