Yeah, i know its weird because that's the concept of the anonymous thread , posting without account, so that makes those threads spam-vulnerable.
I didn't check if you can block sub-threads from the feed. I mostly use the feed for quick access to the new posts and then the "Recent posts" from the main page and the "Show undead posts since your last visit" when logged on. One easy workaround is to subscribe to the "Recent posts" which does not include the anonymous threads.
Edit : Subscribing to "Recent posts" won't work , anonymous posts don't show in the main page listing but when you go to the actual page they do, FML
No big deal, just letting you know.
Certified adarq.org watcher, remember how i caught the google bots by just observing the posts count increase ratio