This was well within Tumblr's legal rights to do, though still poor form for them to have done it, because there seemed to be no legal motivation to "take" the subdomain. The word "pitchfork" is not something that can be trademarked and pitchfork media has no more right to the subdomain than you or I, no matter how badly they want it. So this doesn't seem like a decision Tumblr was forced into for copyright/legal reasons. They just thought it would be a good idea either for profit by selling it or to get on the company's good side (mind you, however, we are only hearing one side of the story, so that assumption may be entirely inaccurate). I don't blame the guy for being a bit upset. Even realizing you have no actual legal claim to something, if you've been using a url, username, twitter account, etc. for over a year and suddenly it's taken from you without so much as a warning, it would be annoying. So no, in reality, nothing was "stolen" from him, but the manner in which Tumblr revoked the URL they had assigned to him feels a bit unethical.