IGN recently posted a rumor regarding the specs of Microsoft’s next Xbox iteration. In it, there was a brief, yet interesting, statement comparing the Wii U to Microsoft's new console: IGN claims that it “will yield 20-percent greater performance than Nintendo’s forthcoming console, the Wii U.”
Though it's no surprise to me that the 'Xbox 720' is rumored to be more powerful than the Wii U, what did surprise me, however (and I think most other gamers as well), is that fact IGN claims that the difference will only be 20%. I think it's safe to say that most gamers had assumed that both Microsoft and Sony’s next-gen consoles would be much more powerful than Wii U. That being said, maybe Nintendo has really stepped up its hardware this time around, which might explain why the discrepancy is not as great as it is with current-gen consoles.
Nonetheless, until we get the final and official specs of all three systems, this is only speculation.