Just because Sony said that the PS3 would have a 10-year life span, that doesn't mean the company isn't apparently moving forward with the PlayStation 4.
According to insider info (along with some speculation!), Japanese website PC Watch is reporting that Sony is looking to alternatives to the PS3's Cell architecture, which some developers have found to be challenging. One early alternative include Cell and Intel's Larrabee. Wanting a bit more horsepower, Sony has apparently abandoned this plan. Sony was also apparently considering a modified version of the Synergistic Processor Unit, but is now supposedly working on designs that include a mulit-core CPU.
Sony, Microsoft and Nintendo are all believed to be exploring new system architecture. And with the exception of a possible Wii HD, PC Watch Impress states that it takes 24 months to produce new consoles, making 2011 difficult for new hardware and 2012 or even as late as 2013 more possible.
However, PC Watch Impress notes that new handhelds will pre-date new home console hardware - so by that assumption, the PSP2 will be released before the PS4.
【後藤弘茂のWeekly海外ニュース】 揺れるSCEの次世代ゲーム機「PlayStation 4」プラン [PC Watch Impress]