I'm bumping this thread because I finally found the Wall Street Journal article that was written during previews about what sets the step-family apart from most versions.
Quote:
As a 90-minute TV special, "Cinderella" was roughly two-thirds as long as the usual Rodgers and Hammerstein show, and accordingly took them seven months to write instead of the usual nine or 10. In many ways they used Disney's animated "Cinderella" (1950) as a template of what not to do—starting with the heroine's "wicked stepmother" and "ugly stepsisters"; in most adaptations, including Disney's, the step-relatives are described as "cold and cruel." But Hammerstein wanted Cinderella's foils to be more human and three-dimensional.
"I was thrilled when they contacted me," says Kaye Ballard, on the phone from her home in Rancho Mirage, Calif. "Of course, I was slightly insulted at first—they wanted me to play an ugly stepsister! But I had a great rapport with Alice Ghostley [who played "Joy" alongside Ms. Ballard as "Portia"], and we made them funny rather than mean."
End Quote
That Flexible Fairy Tale