I've never been a huge fan of blogging for the reasons that he identifies, as well as what I consider to be the somewhat sterile nature of the medium. And I would also agree that focusing on a specific type of writing (especially in a medium where content isn't always the point) does hurt your ability to create longer, more complex pieces (more because you retrain or recondition your thought process to compose short, supposedly pithy blog bits). You may be able to get to the point quickly, but is it the correct point? Have you missed something while rushing to that pithy post?

Not everyone writes or composes in the same way. If he feels that blogging is hurting his ability to perform complex analysis, then stepping away from it is the right thing for him to do. The noise to signal ratio in blogging is far too high, and it's easy to see where that would get distracting.