I'd imagine its people that use Tor that end up getting IP Banned, not that Tor nodes were specifically targeted. I could be wrong though, but that is my best guess.
Yes thats exactly what it is, Theymos has confirmed this before. Somebody using Tor gets banned and every exit they were using gets banned too. But now it's got to the point where Tor is unusable and Tor exit nodes should be auto-unbanned. Perhaps a cronjob that runs every couple of days that scrapes the Tor exit API and removes the IP's from the banlist.
Or, even better, bitcointalk.org runs a Tor hidden service. It would that solve this problem, be very easy to do and the people using it would be protected from SSL MITM attacks, one of which happened to bitcointalk a few weeks ago. Downside is the extra admin time that would be required to run a Tor client.
I'd be willing to donate to a bounty for either of these. Would donate a lot more for a hidden service though!