Have you seen this? http://www.futurelooks.com/new-apple-mac-pro-can-build-better-cheaper-pc-diy-style/3/
Granted, it was almost a year ago, but back then, they tried to build a Wintel machine with the same basic components as the maxed out , and it cost quite a lot more than the price of the (about $2k more). Now, there’s a strong argument that, for example, that workstation-class GPUs aren’t a good choice, or that a machine with different specs would be better, but the old “Apple Tax” argument is usually more myth than fact when you’re looking at the high-end of Apple’s product lines (Retina , ).
Now, if you don’t have $10k to spend on a workstation (or $3k to spend on a laptop) and want to build a less expensive workstation primarily to do game dev work, you’re right that a custom built Wintel machine is almost certainly going to get you better specs for your money than buying a Mac. The equation is a lot more complex, however, if you’re a Mac user already and have a lot invested in software and are more comfortable using MacOS, then you just might be willing to spend more and that’s okay.
I’m not entirely sure why any time somebody asks Mac-specific hardware question on these forums somebody has to pipe in with the whole “You should buy a Wintel machine, dude!”. People here aren’t stupid. Just because somebody made a different purchase choice than you would have, doesn’t meant they made a bad choice. I have both Wintel machines and Macs and for most of my day-to-day work, I’m okay spending more of my money in order to use a Mac as my main machine because I’m more comfortable and productive that way.