As a counterpoint to your argument, I'd say OS X has more professional UI designers than Windows or the Linux OSs and is generally regarded as being more usable too.
Thanks for reading my comment so charitably ;-)
What I'm saying is that beauty to the professional user and beauty to an innocent bystander are different things. A professional actually cares more about usability and certainly cares about aesthetics as they apply to usability. The way a professional perceives a desktop will be very different from the way a casual user does. But some people are self-conscious about that; they don't want their professional exposure to change the way they perceive things, or at least they don't want anybody else to notice. So they want a plastic consumer case for their Hole Hawg[1].
Not that OS X doesn't have a lot going for it on the desktop, but a major part of the appeal for developers is that they can have a great desktop they love without non-geeks thinking they must be a little weird to love it.
Most developers (and sysadmins) I know positively delight in their reputation of being a little weird. I know that given two options I like as well otherwise, I'll usually pick the less common one. I still use OS X, though, having switched from Gentoo in 2003, and having tried Ubuntu and Arch for 6-7 months within the last year.