I'm not sure that's true if you look at growth instead of market share.

Also, how many open source components are used in other OS'es besides windows (which I'm assuming you're referring to here)? If you think of it that way, then most of OSX is open source too. And that goes for a lot of other platforms like mobile etc.

Also, in the server world open source wins by a far wack I think. All the different flavors of open source unix out there I'm sure dominate the web server market.