According to Kotaku, the outfits want to milk the current generation dry before proceeding with the next one. Punters had originally expected both companies to introduce new consoles within five years of their launch, i.e. right about now. However, the economic meltdown of 2008 has forced them to delay their plans.
In addition, the current generation is still doing rather well and unlike last time, there is no immediate need to transition to a new, higher resolution video standard, which was not the case five years ago. Of course, this does not apply to Nintendo and the company is planning to introduce an HD-capable Wii console sometime next year.
Analysts are divided on the issue. Some believe Sony and Microsoft have reached some sort of understanding and postpone the launch of their consoles, while others think that one of them could jump the gun and introduce the next generation in 2013 or even earlier.
More here.