An awful lot of divas use pitch modulators to stay in key. I guess good pitch isn't even a requirement anymore. It used to be you'd get busted if you did a lot of tinkering in the studio because you couldn't reproduce it live, but between machines & prerecorded vocals (lip synching) that's not a barrier, either. Lots of marginal talents become big stars as long as they have a good look (eg Britney, Avril Lasagne, Alicia Keys, etc).
BTW, I'd probably have to list Gwen Steffani as a singer I like a lot. Very unusual voice, you could even say gimmicky. I wouldn't blame anyone who said they didn't like her, but I think she sounds good. I particularly loved her duet with Brian Setzer, "You're The Boss."
I sorta like Sarah Brightmans voice, but her music's a bit uneven.