It is much more convenient to make quick changes to websites from within the web browser anywhere in the world than to fire up an external editor, a SFTP client, and possibly a VPN interface.
I agree with MikeChipshop that a lot of clients don't know how to use (nor want to learn how to use) a CMS. But all my web developer friends use CMS products for even small, static sites even though they know they will end up making all the changes to the content in a lot of cases. This does defeat one of the main purposes of a CMS, which is to allow other people to edit the content.
You should check out Barebones CMS because it specifically fills the "small, static website" niche. Wherever I would hand code a static site before, I now use Barebones CMS. It works perfectly for my needs anyway. Some users have described it as Dreamweaver for a web browser. Your mileage may vary.
Full disclosure: I might be a smidgeon partial towards Barebones CMS since I'm the author but it is a useful tool to know about.