Yes, it is Cliff and Sally's personal story and also the whole pre-Nazi Germany's story as well.
But way back when the show first opened in 1966, Tony Award nominatioons were decided strictly upon billing. If the actor was billed below the title or in a non-spotlighted way they were put into the supporting/featured category which explains why Yul Brynner, Tom Bosley, Tammy Grimes and Dick Van Dyke among others won in the featured category for playing leads.
Joel Grey was below those who were star-billed and Hal Prince wanted to be sure he won a Tony so he kept him there until the day after the awards and then bumped him up to star billing.
It took William Daniels in 1776 to refuse a nomination in the featured category to cause the Tonys to reexamine their stance. Daniels played John Adams, certainly the lead in 1776, and was probably the Tony favorite, but that year they allowed him to un-nominate himself leaving only 3 and the winner was Ron Holgate for 1776.
"If my life weren't funny, it would just be true. And that would be unacceptable."
--Carrie Fisher