The Wii U was one of the most successful launches up to that point.
PS4 and X1 will not maintain these sales. Just like every system, they will drop, nor is Wii U "dead", anymore than 3DS was dead and a major flop destined never to sell and proof that Nintendo would be going 3rd party:
www.vg247.com/2011/04/14/the-problem-with-3ds-why-we-could-be-looking-at-a-failure/
http://www.reuters.com/article/2011/09/13/us-nintendo-idUSTRE78C0PF20110913
Anyone who was paying attention last generation should have realized 2 things:
1. The market is insatiably hungry for games
2. The market will not buy systems until they are cheap
Every single platform last generation sold over 80 million: DS, PSP, Wii, 360, PS3. Some of those platforms took 1-3 years before they ever reached regularly high monthly sales numbers. In fact, the only system to reach and maintain high monthly sales was the Wii. (They did this in the midst of the mobile boom, not before it, despite mobile advocates crying the death of traditional devices.)
And the prime determinants of when EVERY system reached and maintained high monthly sales were a low initial hardware cost, be it the Wii's off-the-bat cheap launch price or after price drops to $299 for the PS3 and 360 and the buildup of a compelling software library (yes, even Wii Sports counts, cultural phenomenon that it was).
While that's not to say one of the two or even both systems, the PS4 and X1, may maintain high monthly sales immediately as with the Wii or PS2, it is to say that while Wii U may never reach 100 million, 80 million, or even 60 million, it is in no way dead. Anyone who is trying to sell you that idea is...
A) ignorant of the market and its history
B) trolling
C) pushing an agenda