I was pondering that as well. My conclusion is it mostly has to do with who the majority of those who used to post those images in the past. I'd imagine that in the past there were probably several users who'd post images of furry, guro, excessive body parts and such for the mere shock and disgust that would be generated by the majority. Most likely they'd spammed the images and generally proved to be an excessive annoyance and so regulations were made.
Frankly I'm more worried that people might get the idea from this thread that because a person disapproves of something it gives them the right to have it removed. The ToS seems more like it's being cited only because it approves their view point. I'd bet if it said nothing they'd be hollering to have it changed to ban the content.