The whole point of consoles is that you can play in the comfort of a massive sofa with mates and a big screen tv.
<rant>You only need to buy a new version of the hardware if you bought something that was designed badly and has an inherent fault. If you really want to of course you could buy one again after a few revisions so that you can have a slimmer case, lower power consumption etc. The key fact is that a game made for the 360 or the PS3 will work on any revision throughout the life of the console which is not the case with the myriad of options (that are constantly being replaced by manufacturers) with a PC build.
Although there have been several versions of the PS3, you won't need to buy another version (in theory) for up to 10 years. My guess is that you'll have upgraded your PC significantly by then and probably replaced it - which is fine if you can afford to do that and don't mind doing it every couple of years.
I've not yet made the jump to a next/current-gen consoles and am still using an original PS2 - the first revision - that makes it almost 8 years old and it still plays all the new games coming out for that platform. 8 years later. Can the same be said for the Pentium 3 at 766MHz with a Nvidia GeForce 2 or Radeon DDR (DX7!) and Windows Me? No?
Kinda makes 300 quid seem like a good deal.</rant>