And by the way, this is not (mainly) because it was front page on HN. HN users do not overlap (a lot) with the target audience for Tumblr. (not a lot at least) HN is of course an important news outlet in the industry.
I think any company can win market, if your local it friend/guy starts recommending you specific brand. For example, I changed 10 peoples mind how to think about AV. They went over from AVG to MSE, because I recommended. Why? Because, there is less chance for them to fuck it up and install trial.