I don't think they want to release a PC, I think they want to release a "computer". I think they see the way people in the home use computers changing, a shift away from PCs, perhaps. Well, it's already happening really, in some respects. I don't think they're really doing it via Linux either, at least not this time around, since it won't be standard. But the main OS is likely to take on more PC-like functionality, crucially browsing the internet. That in itself is not enough in the short term to supplant the PC entirely, but in the longer term..perhaps. There may come a point where all you need is a box that lets you connect to the internet..I think that's a vision that Google has to a point, and it's something that Sony has an eye on with distributed applications. For example, if Google ever put Office apps online as is often rumoured, any machine with access to the internet could be used to access that - including through a standard PS3 browser. So I think Sony may be positioning themselves toward that kind of thing - software running off the network - with more functionality also running locally for the time being - things they think matter more particularly from an entertainment/communications point of view (as shown in that "convergence" slide from Kutaragi's speech - HD streams, movies, games, video communications, web browsing etc.), things they think are important to a "home user".
