Many? What other services do you know of that will be blocked? You speak as if you have a lot of knowledge/experience in this area.

The list of tor nodes is public, and many sysadmins simply import it without thinking much about it. Even though they should only ban exit nodes.

Thanks for that info, I had no idea it was that bad. It's horrible yet understandable, with so many underpaid, overworked sysadmins out there (i can count myself as one of them).