The corporate space isn't dominated by Windows because there are no other options. The main reason for that dominance is change aversion. I'll put it a different way:

When I buy a computer with an OS, I tend to pick Windows mainly because I intend to game on it. If I don't intend to game on it, then OS would stop being a major factor in my decision-making. I might spring for a Mac instead, or I might get a Linux box. It's no longer the point.

If I were buying a computer for surfing the web, I can get what I want. If I were buying it for word processing, I can get whatever. If I were buying it for photo manipulation, I can get whatever. For Door #1, I'd be looking at network connection options. For Door #2, I'd probably be looking for compactness. For Door #3, I'd want graphics and RAM, I think. For none of these is my primary consideration, "Well, the program I'm going to want to run isn't going to be available unless I get Windows."

That primary consideration exists for gaming. If I bought a replacement gaming rig today, I'd get a Windows box. Period.

Another big reason is Active Directory. It's very surprising to me that there isn't a full-featured FLOSS alternative to AD, because what it does is pretty simple, but it works pretty much out of the box, and it scales massively.

Two years ago I would have said another big reason was Outlook, because no other desktop calendaring app comes close (even though it sucks hairy balls as an email client), but nowadays web-based solutions, particularly Google Calendar, are as good if not better.

I think he meant in terms of being the best option available. You would have a hard time arguing that Windows is significantly better than competitors like RHEL in the corporate space. For gaming, on the other hand, no other OS comes close to offering the selection that Windows has, at least for now.