It was in his book, it was more about "just" being a rider on someones technology. No better than Honda as far as he was concerned, whereas Yamaha were more of a family.
In some ways just look how hard Loris has had to ride, with a savage machine under him, apparently in the early days the riders had little input and thats what Rossi wanted, as he thought he was more important than companies slugging it out in a competition of whose technical brilliance was best.

He also mentions that Ducati have more PR requirements for the riders than Honda/Yamaha.