Yeah, I'm pretty sure evidence to the contrary is stronger. A little googling tells me C-levels and founders of forbes 100 are often proflic bloggers. Novell, Cisco, Oracle, a lot of founders of big companies in India, and many here in the non-tech sector blog as well.
Insofar as commenting on HN and other similar sites is quite similar to blogging, there's a lot of others here too.
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.
A significant number of these people and those mentioned in the sibling comments here are not CEOs (if you seek out their job title carefully) and/or don't have startups.
Dalton Caldwell of App.net - http://daltoncaldwell.com/
Suhail Doshi of Mixpanel - http://sufficientlyadvanced.net/
Jack Groetzinger of SeatGeek - http://jackg.org/
Eric Koester of Zaarly - http://ekoester.com/