The PlayStation 2 had its emotion engine, the PlayStation 3 has its technically brilliant "cell" processing unit, the Xbox 360 is closer to off the shelf hardware but even for the time its triple CPU setup was complex and expensive to develop, this is a trend that in our current economy can no longer continue and for once, this is actually a good thing, NVIDIA seem to agree.
In an interview with PC Watch, Jen-Hsun Huang from NVIDIA stated that “You cannot make a game console such as the PlayStation 2 anymore. When it emerged, PS2 had a 100 times higher performance than the most powerful PC. I wonder whether it is possible to make something 100 times powerful than GeForce GTX 680? If possible, NVIDIA will make it,”
It's just not feasible anymore for Sony or Microsoft to bury millions and even billions of dollars into hardcore development of silicone and circuits for the next generation of gaming hardware, not only because of the current financial climate but also because of the effect it can have on overall profits, retail price and take Sony for example who aren't exactly turning a profit at the moment. It makes more sense to use off the shelve hardware, sure the technology leap might not be as ground breaking as custom hardware could offer but off the shelf components bring with them something that (using Sony as an example again) hardware like the CELL CPU couldn't, ease of use for developers.
If the next gen of hardware does use off the shelf components we can expect PC based hardware, CPU's and Graphics cards that are already well established, not the 100x performance hammer blow of the PlayStation 2 era, if we could do that now, NVIDIA would have that product on the market.