Both Sony and Microsoft has made statements that they wanted their systems to extend this generation well beyond the traditional 5 year period. Even if they were lying, both MS and Sony aren't in the best positions to just spring a new system on the console scene at this time. With Sony trying to restructure itself from within, including the ailing gaming division, and just starting to increase its marketshare. And Microsoft focusing a HUGE percent of its companies efforts (including R&D and marketing) on trying to launch a new OS and 'take on' Google.
Even overlooking these points however, there's just the simple timing of releasing a new console. Both MS and Sony recognize that they've been fighting with each other this whole gen, not against the actual leader, Nintendo. And two years ago, they made a complete 180 degree shift in their thinking. They started to incorperate the strategies and ideas of Nintendo and try to adapt them to their model, from 'avatars' on Live to straight copying with Natal and the Wand. All of this retooling is going to drastically change the models of both Sony and Microsofts next consoles, as they try to incorporate the huge markets Nintendo just opened up into their next venture and not just focus on making the most expensive and 'edgy' systems possible to appeal to 'hardcore' gamers.
And frankly, you can't create a console with so many variables quickly. Even Natal itself won't be fully realized by 2011. Even its early release to consumers will only be that of a beta with limited developer support, much like the first Wiimote.
If anything, the next consoles are a long time off. And its more based on the moves of the market and technology which will ultimately lead to one of the major developers to release their system first. And I'm betting that company will be Nintendo.
Six upcoming games you should look into:
