RuffleCrow - I certainly wouldn't want that (I'm a ghost because I like the anonymity), but I guess some would. The thing is, if you're a successful ghost, you can write anything in any voice but you don't have to like it, or even think it's worth publishing. There might be a smaller pool than you would imagine who would want their name on it, or books like it.
Publishers also generally feel that audiences don't like two names on the cover, especially in that format, so it could affect marketing and sales. I genuinely feel that his books making so much isn't a bad thing and, as far as I know, he did write the early ones (might be wrong on that as the publisher who told me might be wrong herself!).