I have worked technical support. I have done it in person, and I worked the phones at Microsoft before they shipped all these jobs to India.

I think most users are quite capable of installing an OS. Most users never call tech support. Otherwise MS woudl be broke.

And I'm willing to bet the kind of users that tend to call technical support are not the kind of users that install their OSs.

That doesn't mean that users that can install Windows and OS X are in the minority. It's just selection bias.