I suspect that people who do not use an autoblock or rappel backup have never rappelled on skinny cords, never rappelled with another person or never rappelled with a haulbag. Probably sport climbers, now that I think about it.[/quote]
Wrong on all accounts (except for the haul bag) in my case. Plus all the people I climb with regularly don't use one either. These people would probably not appreciate being labeled mere "sport climbers", as most are much more experienced than I am, and some onsight 5.12 trad and are responsible for FAs in the Himalayas, among other places. I think you may be on to something however, it that this kind of stuff is being taught less and less in the modern "sport climbing" era.
An autoblock is never a bad thing (incidentally, I had never heard the prusik back-up called an autoblock until this forum, but I assumed this was the true name after hearing it).
But I can't really think of a situation in which a high friction rap device, knots in the end of the rope, and some care would not substitute for an autoblock backup.
"When mountains speak, wise men listen."
-- John Muir