Keith's comment surprised me. I found at least one counterexample among companies we've funded: Jason Freedman of 42Floors. But there are certainly not many.
Look at the CEOs of AirBnB, Dropbox, SpaceX, Facebook, Snapchat, etc. when they were really growing or fighting to survive. None of them seem to blog.
There are exceptions.
But to be clear: if you're a CEO doing something big, chances are you don't blog much. If at all.
Just like you don't go to a lot of conferences and become a "conference ho", as one of your better CEOs once wrote.
I would argue blogging is not a big value add to the startup itself or the CEO.
Someone wise once said, Startups = Growth.
Startups should focus on 5%+ weekly organic growth in revenues or user engagement well after Demo Day when it is much, much harder to grow at that rate.
The rest is not important. Including blogging.