As a person who had a mac for a good long time before installing a Windows OS on it, I'll say this.
As far as mac PCs go, the specs are generally the same as other Windows computers, so anyone that says otherwise is just wrong. And it's true, there is an incredible lack in compatibility with games over Mac, but with good reason. Mac programmers aren't exactly in abundance, and it generally requires a good while to learn how to do so yourself. Companies have to hire specialists at mac programming just to get a game ported, and it's not too cheap.
Another point is that some macs are weird in the sense that one or more parts are fused to the motherboard. In my case, I can't update my video card without getting an entirely whole new computer. I don't really understand why it's done this way. Knowing apple and their $200 logo, it's probably an attempt to fish for more money.
TL;DR
Macs are just as capable as computers running Windows default as far as parts go, though there's the weird case of not being able to update individual parts. There's a very small percentage of games that run on an OS X operating system because of a lack of programmers in said category. If you want GAMES specifically, I would just get a PC, but this is just my opinion. I'm not saying OS X is complete garbage. I still use it for things like music creation, videos, etc.
