It really just does everything.
The first time your favorite console manufacturer comes out with a newer and more powerful system and all the games you already own don't run on it, you realize the value of the PC.
Besides the flexibility to upgrade hardware for better performance and more features, older -- and just plain old -- games still run just as well as (or better than) when they were new.
And the experience isn't limited to the office/study; connect the PC to a 65" plasma and an AV receiver with 5.1 surround sound, put the hardware into an HTPC-format case, and add a wireless mouse and keyboard, a couple of Logitech Cordless Rumblepad 2s, and a 22" touchscreen monitor on the side, and you've got an unrivaled gaming experience.
Besides everything else the PC can do. Which is everything.
And here's one last argument for the PC:
|Can your console do this?|