I built a gaming PC about 3 years ago. Not top of the line, cost about $1000. Haven't spent a single penny as far as upgrades go, and I can still run today's games on high graphics settings. Fallout New Vegas looks amazing. I have every graphics setting on and on high in EVE Online, and my computer never even blinks. I'm only running an Nvidia 8800GTS and an Intel E6600 2.4 GHz with 4 gigs of DDR2 RAM. Most of these parts were just released when I bought them, or were only out for a few months. I've thought about upgrading the GPU to something more modern, and getting the best CPU for the LGA 775 slot that I can find, and even then it'll only be a $600 upgrade to make the computer able to run brand new games on high for another 2 years or so.
Wii launch price: $250
PS3 launch price: $500 (20 gig vesion)
360 launch price: $400
Doing the same buying at release for the consoles costs more then I've ever spent on my computer; I think I'll happily stay with it.