While we all wish for next gen consoles to be extremely powerful and cutting edge, here are a few logical reasons why this really doesn't have to be the case.
1. 1080p resolution displays @ 60 hz
This is the limit of 100% of TV's available on the market today and 95% of TVs sold in the next 5 years. Even the TV's that run at supposed 120 and 240hz, don't actually accept signal higher than 60hz. Therefore 1080p@60fps is the optimal performance benchmark that next gen consoles need to aim for. 4K resolution gaming is not a reality for console gaming for next gen, no matter what Sony and Microsoft end up claiming on the box.
2. Gaming optimized hardware and software
The hardware and software development tools that go in to gaming consoles are very highly optimized and allow devs to squeeze as much performance as possible. A gaming machine doesn't have Windows or some other heavy duty operating system running in the background and a more processing power can be utilized for game performace. Look at Halo 4 and the impressive visuals devs are getting out of 7 year old 360, which at this point has laughable specs in terms of current PC's.
3. Game budgets
The current state of AAA gaming is very expensive and a massive leap in visual fidelity and production is not something that an industry can support as a whole.
4. Hardware cost
Looks like next gen will bundle motion sensers, tablets, waggle controllers and standard controllers. Trying to bundle all these technologies while also offering cutting edge hardware and keeping the price at $299-$399 level is not something 2 out of 3 console manufacturers can afford to do.
Don't get me wrong, I'm not saying that next gen consoles won't be more powerful than current gen consoles, far from it. However we shouldn't be expecting cutting edge high end PC-like graphics performance on paper. When the consoles come out games will look as good as they do on PC and 1080p resolutions, but with lesser hardware.
Remember a console game running at 1080p @60 fps looks exactly the same as PC game at 1080p at 200 fps on a 60 hz display. It actually may look better @ 60fps as you won't see any frame tearing.