The interesting fact about DC's fan club is all to do with timing, rather than popularity.
David Cassidy became a star via television, which had a far greater reach that the limited radio exposure that Elvis And The Beatles got in their heydays.
He also arrived when the 'teen heart-throb' was being recognised by shrewd marketing agents who pushed the 'fan club' idea to the max in terms of promoting him.
Finally, David Cassidy was able to tour far more countries far more often and play to far bigger audiences than either of the other two - which once again exploited his massive appeal.
I am sorry to hear of his passing, I know millions of fans past and present will be sad today.
Sad news indeed....I played 'How Can I Be Sure' and 'Cherish' today on my show, as a tribute to him...had loads and loads of requests.
One of my sister's is particularly upset, as her bedroom wall was covered with his pictures, she idolized him, and saw him in '74 in concert, and even got to touch him.....remember, it made her whole year.