John Romero the creator of ID Sotware; developed Doom and Quake on NextStep! (Steve Jobs Unix based expenso lux computer when he left Apple) presumably why there's always been Linux versions...
"Hey guys - so you want to know why I switched to Mac? Well, the answer is pretty simple: Mac OS X is a more capable environment for development than anything I've seen since NeXTSTEP. And guess what? It really IS NeXTSTEP under the hood.
It's interesting to note that most people don't credit part of DOOM and Quake's success to the platform we developed those games on. But it's really a big part of the success of those games because NeXTSTEP freed us in ways that MS-DOS could never have achieved. Even cross-compilation of our code was a really sweet perk - all we had to do on MS-DOS was run the executable and it automatically bound to the DOS extender and the game ran. The game EXE was compiled in NeXTSTEP and saved to a network drive.
Today there is absolutely *no reason* to develop on PC hardware. You can run Windows XP/Vista in a VM Fusion window on one of your Spaces while the rest of your Mac runs native. When you need to do Windows work, just switch over to that Space and you're there. You can have other Spaces with other OS's such as Linux in them as well. The Mac can do them all - at native hardware speed.
For a programmer, coding in Objective C is just heaven compared to development in C++ in Windows. I'm not knocking Visual Studio - I totally love that product and used it happily for many years. But Cocoa development is way more fun and easier.
Apple's unified User Interface across all their hardware and web really shows that the company has a very clear vision for their product line and they've accomplished something that no other company ever has - and that's why everyone is switching. Their UI is FUN and EASY and does what you expect."