As far as I know, it was created by Norm Pattiz who was in charge of the network and loved the idea of Casey joining Westwood One. It didn't necessarily have to be created the same way as AT40 as it was already being done.
To my knowledge, Don Bustany and the original AT40 folks had zero hand in Casey's Top 40.
Right. I think a reason Casey never gave a creator plug was because it'd be embarrassing to admit you didn't create your own countdown when your name is in it. "Casey's Top 40 was created by Norm Pattiz for the Westwood One Radio Networks." Although I could imagine him pulling this off: "Casey's Top 40 was created by Norm Pattiz, based on a format created by Casey Kasem and Don Bustany."
Although when I think about it, didn't Casey did take a number of people from AT40 to CT40? I heard Merrill Shindler's name mentioned in a 1984 credit roll.
I remember that Ryan Seacrest used to mention AT40 was created by Casey Kasem and Don Bustany. But he hasn't said that in several years, and to my knowledge has never credited anyone else on the AT40 staff as Casey and Shadoe did.
If you listen to a Ryan show from 2004, he does the same full-credit read that Casey used to do.
I always thought it was weird when Casey would announce in third person that he created the show.
And Caseyfan.. Ryan brings up Casey at least once every 2-3 months on AT40, and always in a respectful and good light. The only thing Ryan and Premiere like to pretend didn't happen is the Shadoe era. Casey is highly respected over there.