What is your definition of 'only slightly more power'? To me, if Wii U is even 2-3 times 360 on the bullshit scale, it's slightly more powerful, because of diminishing returns. It's isn't meant to be a disparaging comment. I'd be happy with that boost. But it still wouldn't put it in the same league as medium-to-high end PCs already on the market, nor do I think it is realistic to expect Sony and Microsoft to bring out new machines in that range. That's all.
Now people who are writing off the Wii U merely on the basis of the Wii and how it lacked horsepower compared to other consoles... meh.
I am personally expecting WiiU to have a GPU that is around 1TFlop. I don't know where that puts the WiiU in terms of bullshit multiplier, but I consider it more that slightly powerful than current gen.
How that turns out when we think of diminishing returns might not be that impressive though to the casual user if the WiiU can't handle DX11 features, but that extra boost should be able to render all current gen without any of the sacrifices made to frame rate and screen tearing.
When people say only slightly more powerful than xbox360, it more often than not comes across as meaning no visual boost to rendering capabilities. Which I just don't understand.
But this is all speculation and it all comes down to what kind of GPU wiiU has. We don't know much but the main point is people are just expecting little improve, which seems to be guided by a bias than known facts.
And i don't expect ms and Sony next gen systems to be super powerful.