Actually I don't agree that it's always the presenter that pulls in the viewers. I think the programme format is much more important. For example, people who listen to The Today Programme listen because they like The Today Programme. See also Strictly Come Dancing, The One Show etc.
I do think there are a few exceptions to this such as Claire Balding, Graham Norton to name two, where people a tuning in to watch them. But only when they're the show; not just when they're hosting a show that anyone competent presenter could host.