I sell drupal sites for fast deployment for less, while I make my own projects on my own time using various text editors like notepad+.
So as a hobby, your son should keep doing what he does. But as a job, customers usually want everything they see on every other site: login system, blog, forum, image uploads, file uploads, statistics, email notifications, captcha, twitter facebook integration, comments, site administrators, wysiwyg editors, ajax, browser compatibility, sql injection proofing, etc.. and they want it all working like a charm like tomorrow!!!
Anyway, my final advice would be not to teach him computing at all, it's a dead end, cheap job, only to be seen as a hobby.