As someone who uses OS X, Windows, Linux, and a few other *nix systems, I see the utility in each.
In terms of Windows, its primary use seems to be as the base for MS Office, which runs better as a fat install on a native Windows install than in any other configuration. And that's not a bad thing - Excel for Windows, for example, is a pretty profound tool, better by far than either cloud versions or what they've released for OS X.
OS X's utility is in its ease of use especially on portable systems. It's not uncommon in my environment for a user to use several different systems -
- A Windows system (either local or a virtual session)
- a Citrix/NX client to a Linux system (usually but not always a VM, and generally not dedicated per user)
- a Mac - often an Air - with which they attend meetings and connect to Windows or Linux systems
The staff uses each platform as needed....there are die-hard Windows and Mac and Linux users who scarcely ever use the other two, and there are people (like me) who switch easily.
And Windows 10, just now starting to get into the mix, doesn't seem to be horrible. Haven't found obvious limitations yet (but haven't been using it long). We'll see how it pans out - I'm suspecting, like Win7, it won't be a really big splash, just gradual expansion into the Windows part of the enterprise.