The site was more opinionated than your typical "isup.me" style site, so while I can't justify the C&D I can at least understand the motivation a little bit more.
Although there's probably some Streisand Effect happening here. I hadn't heard all this about Tumblr - but now it's the most memorable thing I've heard about them. It's bad PR, but as others are pointing out, it's likely Trademark protection.
Totally agreed. Just a "Can you be less snarky please? and I would have changed the language and redeployed.