Well, the funny thing about Apple's OS X is that it's wildly popular with technophobes and deep nerds, and not a lot in-between.
Designers and filmmakers don't give a flying monkey about how closed the system is, they just like having their tools on a stable platform. And deep Unix nerds like having an easy version of Unix on laptops. Or as one Unix Admin friend of mine put it back in the day, "Hey man, you have no idea what it means to have a version of Unix on a laptop that just works."
I do 95% of my work in a Windows environment, so I should probably just shut the hell up.
-edit-
Here's a not-terrible whitepaper about the architectural differences between Windows and Unix. Still looking for some sort of handy graphic that can illustrate the big differences. Still failing.
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