I agree that we should take the accusations with a grain of salt. That being said, let's assume, for now, that they're all true.
1. I'm glad Kelli didn't get the Tony. Isn't there a superstition that when new stars win awards, their careers end? They're too associated with that first role. Kelli now has a more supportive fan base, angry that she didn't win. Sara Ramirez has people hating her because she took the Tony away from Kelli. Her career was probably trashed before this whole missing-performances thing.
2. Gwen Verdon - was a dancer. She did extremely arduous dancing that without a doubt took a toll on her physically. I'm sure she sustained injury from it. So, in that respect, it makes sense that she missed performances, especially as she got older. As for her voice? She was basically a non-singer doing fairly strenuous vocal work. Again, as she got older, that must have had a negative effect on her voice. None of this is true of Sara.
3. Donna Murphy - was already a name when she started missing performances. She sort of had that freedom.
4. Audra McDonald - Well, I've never heard anyone like her. If someone wants Audra's voice, they really have to use her. So her career couldn't die. Sara, sadly, as talented as she is, is kind of dime-a-dozen. Also, Audra does operatic material - which, to my knowledge, is more difficult to sustain 8 performances a week than musical theatre.
5. If Sara's having voice trouble, why doesn't she just fake her high stuff? That's what Idina did (no, she didn't sing that F every performance, it got gradually lower during her run).
6. That was long. phwooh.
theatre.