And Buran(soviet copy of the shuttle) could and in fact did fly completely unmanned. In a way it's a shame the collapse of the soviet union killed that program, because a crew less shuttle would have been a huge asset to have.
I'm not surprised more people don't know about the X-37, but it's in effect the distillation of the Shuttle program to a very effective vehicle: Crewless, reusable, cheap, and effective.
Bureaucratic requirements and institutional jockeying largely ballooned the Shuttle into something it was never supposed to be.
