Comment by jppope
Maybe just me, but authors gravitate towards certain formats that fit them. Oscar Wilde did great with Dorian Grey but it was nothing compared to his plays. Imagining J.K. Rowling writing a blog feels wrong. I get Gwern's perspective, I'm not sure if I would read a gwern.net book... but on the flip side Randall Munroe (XKCD) has a couple of great books. So who knows?
JK's a prolific micro-blogger. I'm not sure her tweet engagements have surpassed her book sales yet but sure feels like we'll get there at some point.