Also useful would be the cost of expansion of features. For example you can use ANY headset with the PS3 (USB, a bluetooth set you have for your phone, whatever), you can use ANY 3rd party hard drive (I got a 250GB 2.5 inch HD for my PS3 for 80 bucks, took me 30 seconds to install+10 mins to transfer my saves and other things) and you can install Linux on the PS3 and use it for anything you want.
For reference the 20GB 360 drive is almost 100 dollars, the 120GB drive is almost 200 dollars (more then twice as much as expanding the PS3 to 250GB for half the space. 360 has a four times higher cost to GB of space ratio). There are even 500GB PS3 drives now for around 200 dollars. Sure a terabyte is just around the corner.
The 360 has a low base price, its like a Yaris. Sure its cheap out of the gate, but if you buy all the stuff required to make it equivalent to a nicer car it ends up costing you MORE to get the Yaris then the better car with more standard features. 360+wireless=the same price as a PS3 with far less features and less expandability.