(Caveat: it's almost been a year so it's starting to show its age in some new games. But that's not really something you can get away from. I'm also concerned that the next gen Macbook will only offer an integrated Iris Pro chip instead of Nvidia switching. Don't get me wrong - Iris Pro graphics are impressive, often performing at up to 66% of the Nvidia chip - but it will almost certainly be a performance regression.)
I'm not sure what you mean here regarding the OS. You can install Windows on any Mac since Apple transitioned to Intel processors around 2006-2007.
>So if the laptop is going to be used for gaming, then it does not make sense to buy a Mac and install Windows on it.
Are you sure? I think even if you cannot utilize the touchpad and energy efficiency to its fullest capabilities (which are not really relevant in gaming anyway), the build quality of the shell and the quality of the screen and keyboard makes it a strong contestant even among normal Windows laptops. Plus, you have OS X there (or Linux, for that matter) for non-gaming uses.
I've been playing modern AAA games on Medium graphics settings at 1080p (or sometimes 720p) with very good results on an original Retina MacBook Pro. Could I get better graphics with a different machine? Totally, but it's good enough that I don't feel like I have to own a separate gaming machine anymore, which I'm very happy about.
