You mean I can't play my Windows games on my Mac?
By no means I know a lot about Macs, but I'm pretty sure there are some games that are not compatible with Mac. Also, Mac's specs are ridiculously low - the fanciest 27" iMac with i5 worth of $2k has NVIDIA GeForce GTX 675MX as a video card which is a good mobile chip, but comparing to desktop cards it sucks balls. It also can't handle some games which makes some Mac-compatible games worthless since you can't play them anyway.