>Since, as this article says, Tumblr's business model is depending on people using it, removing comments (in favor of pushing people toward reblogging) seems ill-advised.

They've recently added a chat system. http://i.imgur.com/Aw8EEvh.png It's the smiley face in the middle. I don't know if it's default yet but I have it right now and it works fine. The only difference is that in a chat system comments aren't public, but if you're giving other people feedback this works fine. I think this is a good middle ground between the network effects they get with reblogging and just being able to give people feedback without spamming your followers.