How many other IPs have the advantage of 30 years of nostalgia? I've learned not to trust review scores on Mario or Zelda games, because even if they were bad (*coughSkywardSwordcoughcough*) they're still going to get great scores for fear of crucification. And that's not even something without evidence, as we saw what happened when Jimquisition gave a review on BotW. And while fan backlash against middling reviews isn't exclusive to Nintendo IPs, dammit it was a whole lot more intense when Zelda got a 7 than when God of War got one.
I have no doubt that Smash and Pokemon are going to rock the industry, though. Smash will probably review an MC of 85-94, but Pokemon will likely suffer from the casual aspects and get an 82-87.
A game being on the Wii U matters significantly less than it being on XB360 or PS3. It's harder to expect someone to rebuy TLOU when it sold gangbusters on a system with 80m+ users. But the Wii U didn't even break 15m. It has less than an eighth of the people who bought PS3/XB360, so people are significantly less likely to have played Mario Kart 8 than, say, Prototype. So it's not that Nintendo fans are hypocrites, it's that new and returning Nintendo fans are getting a chance to try out great games that they missed.
Except most of the mainline games have averaged around that particular score, 82-87. Ultra Sun/Moon has an 84 Metacritic, Sun/Moon have an 87, and X/Y have an 87/88 Meta.
As for the other bolded part, I agree. Only about 14-15 million people owned a Wii U. Bayonetta 2, DKC: TF, and Captain Toad kinda suffered sales-wise so giving them a second chance is nice. Heck, didn't people here want Xenoblade X and Tokyo Mirage Sessions ports for Switch?