Do you think it would suffice to just buy a computer labelled "gaming pc" and just check the specs against the recommended specs posted for each game?
Also, once the PC is acquired, is it simply a matter of upgrading the graphics card every year or so and leaving the other components as they are?
You really shouldn't go prebuilt. I've heard many horror stories of people thinking they were getting a gaming PC only to find out what was inside was junk. You are better off building your own but if you refuse to do that and do want to buy one built. try used maybe. just makes sure you verify whats in it before you buy it and make sure its actually a gaming PC.
Specifically the GPU.
PC game sales= more games then you could ever dream of owning. PSN - ArkonBlade XBL - The Wolf Shadow STEAM - ArkonBlade