I'm kind of surprised more people don't "get" why people keep buying more of a given console after repeated failures.
It's mostly because your gamer tag/user ID and more importantly, because your account, which gives you access to everything you bought on XBL/PSN is probably worth a lot more than a $200 box if you've been gaming on a given platform for years with any sort of regularity.
I'm pretty sure I have several hundred dollars worth of games and content on PSN from almost 6 years worth of purchases which means if I ever want access to all those games and content, I have to have a working PS3.
There are a shit ton of users on XBL in the same situation, so it's really not a matter of "why do I keep buying replacement consoles" so much as you have to in order to access your purchases.
That's probably the thing I like most about Steam; I can run it on any PC I build or buy and I'll always have access to the hundreds of games I have bought through the service no matter what happens to the PC I happen to be using. Whenever one breaks or is ready to be replaced, I'm actually happy to be given an excuse to upgrade.