I'm not sure that it is. Linux is doing better with gaming, but it still doesn't have enough dev support.
Luckily, I think this will change. Mac is a niche player, they won't ever have a substantial market share, nor do they want it. Whereas Linux is incredibly versatile, and with proper development, could actually go head to head with Windows. All it needs is the PC equivalent of Android... a couple of big, successful products developed by large manufacturers and tweaked for user friendliness. Ubuntu tries, but it doesn't have the resources and is currently bogged down in stupid shit like Unity.
Not only that, but Linux is being adopted by most of the third world, and seeing some success with the first world. Whereas Windows, particularly Windows 8, doesn't seem to be doing much for people. Steam for Linux was developed because how much they hated Windows 8, and Gabe said he thought Linux had a bright future.
Of course, Apple fanboys will be Apple fanboys. Good products but seriously overrated.