* Students looking for a stable and/or sexy device for their university.
* Artists using applications that don't exist on other platforms (or that prioritize Mac platforms).
* Hackers that want a Unix-like system with a BSD userland, or want Anything But Windows on a laptop.
Sadly, these groups are small groups with eclectic needs that won't be met or improved by real systems engineering with the kernel and core modules. What do I mean by real systems engineering?
* Major kernel development
* Novel and/or modern filesystem support
* Fundamental or deeply integrated "platform" features
In Linux land, every major kernel release brings these features. There are tangible improvements to filesystems, to core features that enable new things to be developed on top of them in every Linux release. These are, largely, absent on OS X. The system is too closed, and the result is that things like Time Machine or even security features and ACLs are hacks upon hacks. Full disk encryption and home folder support is, again, hack-ish, and largely built on work other people did. OS snapshots is essentially an "rsync" to another drive with a smart "restore" utility that repairs changes.
The major kernel development that Microsoft undertook with Windows Server 2003 and Vista is still paying dividends. Folder shadow copies became integrated into fully consistent backups with built-in snapshots. Full disk encryption improved - though home folder encryption is still tragically stuck with NTFS "EFS" support (lackluster, at best.) UAC, AppLocker, and integrity levels brought foundational improvements to the security model. Networking stack changes brought DirectAccess, a woefully underused and under-marketed technology. Storage Spaces and ReFS, though years too late, are interesting alternatives to ZFS/BTRFS. Transactional NTFS was woefully underused, but maybe it will return with ReFS. The core improvements Microsoft is making to the NT kernel are still worthwhile, though. Hyper-V is a fantastic technology, and could really blow people's minds when it's baked into the client OS. (For reference, Hyper-V powers the Xbox One's dual app/game personality. It allows isolating the management OS from games running on it, and also keeps the management OS from interfering with game performance with resource limiting. And they both share high performance access to the GPU.) Ah, I could go on. Reading about new stuff in kernel development is a joy.
Of course, I could go on ad nauseum about Linux changes since 3.0x, but http://kernelnewbies.org/ does a better job than I will.
The result is tragic: Microsoft invested in platform features and then didn't sell users on what it could do with Vista. Apple continues to apply lipstick to the OS X pig and sell users on changes to the window manager and built-in applications.