Sony's in a pretty rough position because they have to keep the PS3 alive for (at least) 4 years and it has to sell at a respectable level ...
When a console fails it introduces doubt in consumers, developers and retailers which dramatically hurts your ability to sell future products. Consider Nintendo, with the challenges Nintendo faced with the N64 and Gamecube, and with the impending release of the PSP, Nintendo had a great deal of difficulty finding third party developers to produce Nintendo DS games. Even with the success of the Nintendo DS, Nintendo still had difficulty convincing third party developers that their approach with the Wii was compelling ...
If the PS3 doesn't get to a respectable level of sales and doesn't have a reasonably long life Sony will be unable to launch a PS4
