Belle De Jour answers my question

Blog! The Guardian News Blog is carrying a brief interview with Belle De Jour:

"JP: Now that you've stopped being a call girl and (largely) stopped blogging, why not reveal your true identity?

Belle: Because I still have a family who speak to me, and would like to keep it that way. Also, if my identity became known, the publisher would probably make me do a book tour. Eek."

So the enigma continues.