First, the mere fact that you suggested he used his mac for gaming is LAUGHABLE. Macs aren't for gaming. That's why I own a PS3. PC gaming is more expensive than buying a Mac for personal use.
Your entire argumant is based on the assumption that both the PC and Mac are being used identically (e-mail, web, office suite, etc.). When you take one out of a particular arena (in this case gaming) your argument falls apart.
I am amazed at your last sentence. Are you saying that you have spent more than a $1000 (price of a moderate mac) to get a PC ready for gaming?
Don't forget that it is gaming that drives PC evolution (getting more fps, 3D depth, etc.). If all we needed a PC for was spreadsheets, web, and e-mail, they wouldn't have the horsepower they have now.
For the Mac it is horsepower for graphics/film that has driven its evolution.