Can one person own over 400 websites and operate all of them by there self!?

I read somewhere over the Internet that some guy said he own over 400 sites and does all his work such search engines optimization, keywords and etc... Is this possible and how does he do it. The only thing I could think of is through sub domains, but as far as my understanding of sub domains only work with your master site and you're just add on to your site like a blog. Help me Guys I'm puzzle about this one. Take care and God bless.