There's a bit more to HSC than most other solutions, particularly when
it comes to verification of hotspots. You can specify screen
coordinates relative to a bunch of other landmarks, verify colours to
be reasonably sure you're clicking the right thing and account for
differences in window size etc. Then there's spot rings and the
ability to communicate directly with the JAWS API so that you can
pretty much build a custom user interface if you know what you're
doing. Probably a heap more stuff that I'm missing too. Most HSC sets
aren't, but it can be super elegant for a bolt-on solution in the
hands of someone who cares about UX.
Note: I'm not plugging it as a fan boy, it's more a case of being
frustrated that this stuff can't be done with any other screen reader
yet so far as I know.