[declan]

Craig and Mark are owners of companies or sports franchises (or own large amounts of equity in them), but are not CEOs. I'm not aware of the CEO of Craigslist, Jim Buckmaster, blogging. Nor am I aware of 2929 Entertainment's CEO, Todd Wagner (co-owned by Mark), blogging.

Also on some of the other folks listed in sibling comments, like Richard Branson, I'd be very surprised if he were the one posting on the Virgin "blog" under his name. Just as executives and politicians have speechwriters, they also have exec comm and marketing staff to write blog posts.