Especially with Steam sales games can be REALLY cheap for PC. Heck, a couple months back I got Mount & Blade for $7.50. If I had gone on an Xbox with that amount of money, I probably couldn't even download a map pack let alone an entire game (which gave me over 60 hours of entertainment so far).
I would wager that if you buy games mostly on sale on Steam, if you combined the price of a mid range machine and games, over the lifetime you would probably be spending about the same as a console and its games. Hmm... lets try a little theoretical math...
Keep in mind I don't know to much about console pricing, so this is just a general estimate...
I will use an average of $30 per game for PC, since if you use digital distributers that is probably about what you will spend on average w/ their frequent sales.
                  Console                 PC
----------------------------------------------
  machine|  $300-$400       |    $1000
per game|  $50-$60           |    $30
10 games| ~$550              |   ~$300
20 games| ~$1100            |   ~$600
30 games| ~$1650            |   ~$900
----------------------------------------------
30 games|  ~$2000          |   ~$1900
+machine|                       |
So if you buy around 30 games per hardware lifetime (about 3 or 4 years) a PC will be about the same price as a console. And likely a $1000 PC will be able to run at higher graphics settings. These are rough estimates of course, but they do make my point. Also note that I do not take any paid DLC into account, which would also likely add up to at least another $100 for most console owners.