I wouldn't even call them "Tumblr themes." These were just blog themes, owned by a third party, who licensed them to us for use on Posterous. They just happened

I wouldn't even call them "Tumblr themes." These were just blog themes, owned by a third party, who licensed them to us for use on Posterous. They just happened to be on Tumblr first, but don't have any other affiliation to that service.