Let me explain ...
Like AOL, Facebook is a walled garden reproducing what is standard and open on the web/internet as a whole. AOL had AOL email, Facebook has html homepages, and RSS/ATOM
But "people" cannot create their own content - they cannot write HTML, host web pages etc. But contenteditable fixes all that - and with the clever Dropbox tie in, anyone can start with a templated page, drag and drop images from their own desktop, (#) and publish themselves.
(#) oh yes drag and drop images onto a web page - its soooo cool. Aloha supports it at least.
Also, there are a lot easier ways out there to publish your own content online (Weebly, Tumblr, etc) but that doesn't seem to have stopped Facebook.
Whilst it is of course possible to replace a CMS with flat HTML files what is the main target Market you see for this?