But that same reason to prefer a standalone stereo works for a standalone DVD player versus a PC, and a standalone media box rather than a media PC. PC's are faf and overcomplicated for most people's use. Yes, they are far more flexible, but most people don't need that. A box that plays your discs and download content, and interfaces with your portable devices, and lets you record TV and play games, without the complexity of a full blown OS with drivers, utilities, competing applications and the like, has a lot of appeal. From my experiences with these devices, PS3 is far better than an expensive Media PC in almost every way for my interests. A friend upgraded his MPC with the latest ATi GPU and DVD playback software, spending an extra £100 or so on noise reduction, and the result was far louder than PS3 and with a 'bug' in the software that means DVD's are rendered in naff-o-vision with red's banding and blocking to a horrific extent. This was apparently a change in the software as it was 'upgraded' for 'security reasons' so it has to use the GPU hardware and not a software renderer.
As a would-be owner of a media box, PC is too much effort. PS3 isn't perfect, but it's very close to the ideal solution for less techie folk, which is the majority of people out there. A properly developed system that does PVR and media playback of the major formats without needing a half dozen different boxes or a problematic PC is valid idea IMO. Sadly the creators of would-be solutions tend to go with overcomplicated too, resulting in hardware incompatibilities between TVs and players etc. Even a TV isn't just a TV any more, but has pages of options to worry about.