This assumption, like just about everything on that site, is about 15 years out of date. A whole lot of "clueful" people have given up on running their own mail

This assumption, like just about everything on that site, is about 15 years out of date. A whole lot of "clueful" people have given up on running their own mail servers for their personal email accounts. They either use Google Apps, if they want their own domain, or they just use Gmail. The spam problem is too great otherwise.