They're also the reason that developers spend time optimizing their game properly and the reason that I can play new games on my older rig.
I don't have the money to keep upgrading my computer. Some of us have to buy food and pay rent and whatnot.
Of course having to upgrade your hardware can be quite costly. But I don't agree that because of consoles we have better optimised games. Because that is simply not true. The reason that you are able to play 5 year old games is because the graphical innovations have been very lacking.
Even Battlefield 3 hardly looks good if you consider that most of it's beauty comes from high resolution textures and a whole bunch of shaders, because the amount of polygons on some of the objects is nothing to write home about.
If anything, the consoles are the very reason that most games aren't optimised. Many games start off with a console as the leading platform, then the developers try to port it to the PC to gain some extra cash, but they tend to spend less time optimising it for the PC since it's not going to sell as much as on the consoles anyways.
You'd think that this is the fault of piracy, but actually it's more the fault of developers thinking that gamers actually want games that severely lack content due to the limitations of console hardware.
Yet publishers will do everything in their power to blame the consumer, I just know that when a game is good I will buy it.