What's (allegedly) hard to grasp is that Tumblr is Tumblr, not a generic money-engine that eats X dollars worth of fuel and puts out $Y worth of value. Mayer is acknowledging that part of Tumblr's recipe for spitting out that $Y is the culture that the users and the team have made, and that approaching it as if that didn't matter will not work.

Whether that's how Tumblr's integration into Yahoo! will actually be treated remains to be seen.