Computers can be upgradeable. That's often cited as an advantage PC's have over consoles. But it's not really an advantage. I mean, the Xbox 360 launched in '06, we're in '13 now, that's 7 years, without the hardware changing. If you spent $399 on your Xbox back in '06 and it never RROD on you, then you're still playing latest games at top quality. There is no computer you can build right now that for that price tag can last you 7 years. The thing with consoles is that games are built around the platform, optimized for the hardware and software, and then ported over to PC. Most games are built like that, and so when they finally get ported over to PC we get HORRIBLE efficiency compared to the console, which basically is why consoles manage so much better graphics with comparably worse hardware. And as time passes, dev's get more familiar with the platform and get better at optimization, and hence can squeeze out a little bit more performance out of the console, resulting in games with acceptable graphics even if the console is 7 years old.
Computers can do that? Sure, if you build a $3000 computer, it's probably going to last you 7 years. But build a $1000 machine, which is a very good range for a powerful gaming rig, and see if it can run latest games for 7 years. It won't. For the first 2 years, you'll be running everything on max or near max. Then, the years start to show, and you're now forced to not use the highest settings graphical goodies, like PhysX or HDR and Full Particles. After 3 years, you have to start tweaking graphics down some more in order to still play with highest texture settings. After 4 years, you probably can't run the latest games in high texture settings, even when turning down every option in the book. After 5 years, even medium everything starts to impact performance somewhat.
That has been my experience, with the computers i had over the years, which had all been on about this price range. After 5 years, they became mostly incapable of keeping up. And i STILL spent more on them than i had spent on consoles. Now, i could've upgraded, sure, put a new graphis card and all is well. But a new graphics card, a good one, isn't less than 300$. And to keep up with "always highest" settings, upgrading is not always the best option.
About the death of the PC... The statistics show that PC sales have been dropping. Steadily. Tablet sales are increasing, Smartphone sales are increasing, and Ultrabook sales are increasing, but Desktops? Steadily DECREASING.
Intel announced a major change in their business model. It also did so in response to rage from it's shareholders because the company has been experiencing shrinking profits... After Haswell, their next line, Broadwell, will be soldered onto motherboards. Sure, it's rumors at this point, but there's very good reason to believe that. AMD also has been heading into a very different direction with it's Trinity line of processors.
Bottom line is: the desktop is going to be replaced relatively soon. The days of the Workstation are nearly over...