I would have gone even further than you did in answering to “Anne”.
Book proposals presented to agents and then to publishers must contain marketing plans at least as strong as the actual material being proposed for publication.
There might have been a time when major publishers had sufficient resources themselves to promote a famous person’s book.
They no longer have those resources to throw around on risks.
If Oprah herself presents a proposal with no marketing plan, and the publisher receives a proposal from Justin Bieber with a very persuasive and plausible marketing plan, committing Bieber personally to promotion of the book, the publisher will go with Bieber before Oprah.
I’ve ghost written proposals and then books for several people just one notch down from those two on the pop culture fame ladder. Strong marketing plans in the proposals made all the difference, not just in getting the book proposal accepted but also in the size of the advances.
I always opt for more money, rather than a simple “as told to” credit, or anything like that, because in the long run, I don’t care to be known as “so and so’s ghost writer.”