The discrepancy apparently comes from a change in the way the state department defines terrorism. The 774 figure defines terrorism as an international act and comes from Patterns of Global Terrorism by Berkshire publishing. The larger figure comes from when the that definition was widened to include acts of terrorism within borders. Had I known this I'd probably have picked a less controversial comparison, though obviously it brings up the question of what terrorism is, which I think is interesting in itself.
I had originally wanted to compare the health care deaths to terrorism deaths in the US, but even taking the loosest estimate 17 or so to 45,000 is too big to illustrate!