Interesting thread going here, though it would be nice if a few contributors could cool their heads enough to keep it civil. In any case, concerning when new consoles might come out. One thing you need to consider is the cost of development.
From all reports, sony dumped billions of dollars into the development of the PS3. Who knows how much microsoft has dumped into xbox360, but I would assume that they still haven't broken even yet (even if they are making money now, they still have to make up for all the money on development and on selling the console below cost...). On the other hand, Nintendo is selling the Wii at a profit, in fact they've always sold their consoles at a profit, though it's probably because they don't have the deep pockets that sony or M$ do.
So what this tells me, from a business perspective, is that Nintendo will break even on the development costs long before either of the other two. Once they've broken even and are actually making positive income on the wii, they can start dumping money into future development. Sony on the other hand has a very very long way to go before they break even, and every console they sell puts them deeper into the hole, instead of digging them out. It would be a pretty poor business decision to start developing a new multi-billion dollar console before the previous one is even paid off. Microsoft did it once, but I doubt even Billy is willing to dump millions into a business that never makes money.
Anyway, I bring this up because it puts a limit on how soon Sony (or the other two) can develop the next systems. I could be wrong I guess (I'm not a Sony exec) but I can't see them starting development on ps4 at least for several years (at least not serious development). I doubt Sony shareholders would approve...