It gives me the ability to create something for a client that allows them to do what they want without having to pay me or a code monkey to do the ongoing updates.
Well these sites are owned and managed by myself and I do not build sites for clients.
But I do agree, It would be difficult for a client to upgrade each module/theme in drupal... but I guess Drupal 7 will solve that issue by making the system upgrade automatic.
Whats interesting to me is that many people use a variety of CMS's while I can barely keep up with one. + I prefer to focus on one CMS and learn the ins and out rather than playing around with a couple CMS's.