Quick look at the profile (unless you recognize the name) reveals Gregory is the founder of ReadMe.com (when you guys moved from io?!), so supposedly ex to start his own company!
"The problem with not having the .com of your name is that it signals weakness. Unless you're so big that your reputation precedes you, a marginal domain suggests you're a marginal company."
I'd say there's a few major reasons: protecting the name and signaling we're a real company to larger corporations.
For us, we also host websites that allows JS/CSS/HTML, so being able to put our assets on a separate domain helps with security issues.