What does FB provide that you don't get with a combination of email/USENET/blogs/chat? Branding, janitors, and indexing.
Branding is useful because these things are so scale-driven that you want to be on the one that everyone else is using. It's easier for the uninvolved to figure this out if it's the one with huge advertising billboards.
Janitors are a necessity. Some are human, some automatic. People want spam to be fought, and they want abuse to be removed.
Between those two is the "nudging" of people into how to use Facebook. Why should you post life updates? Because it's the "done thing".
Indexing is useful because it enables you to find people you want to get in contact with using their human-recognisable name. (Facebook occasionally undermines this by refusing to accept names that people are known by)
Both of these are ongoing effort that has to be paid for if it is to scale and be done properly. Hence all the underhand cash-extraction processes.