I concur with r.j.s. I have Win7 in Boot Camp on my iMac for the sole purpose of playing an occasional PC game and it works great. Actually looking forward to the new SimCity game next year too.
Haha, I think it's more that OS X has a significantly smaller games library when compared to Windows.
Personally, I prefer having my dedicated Windows desktop for playing games on and use my laptop for university. Perhaps play the odd bit of SWTOR on it from time to time.