Yeap, why do you think they have twitter accounts/Facebook. It is not a desire to mix with the great unwashed but to sell either a chocolate bar, a book, a DVD or tour!!! Half the time I am convinced it is all down by a secretary in a Public Relations Office, signing off at Robby Williams, Katie Price etc etc etc
Maybe for some but not for all. Top crime author Ian Rankin keeps us up to date on his doings: concerts he goes to, new pubs he tries (he's a great lover of rock music and beer) and on the process of writing his books.
Also, lots of the Doctor Who cast - new and old era, interact with the public and answer queries, talk about things, etc.