"...Microsoft made significant improvements to their security model by showing (by default) UAC prompts..."

I wouldn't call nag prompts that people learned to reflexively say ok to a significant increase in security. I don't know of any hard data (couldn't find any), but anecdotally, I see people just pressing "Allow" without any thought because it comes up so often.

Yes, it's similar to the unix model, but people using unix probably have a much better idea of what security means and what the risks are going in.

EDIT: I just realized that you may have said that sarcastically...