In my fourth year of my PhD on schizophrenia and I'm currently writing up my thesis. I'm procrastinating right now so thought I'd do something useful with what I've been studying.
And no, schizophrenia is not multiple personality disorder.
Edit: I have to get dinner and run some errands. I'm really enjoying this so I will definitely get back and answer the rest of the questions.
IME that's more a matter of stigma. People in the US who hear voices in a way that isn't immediately threatening are less likely to tell others about it because of the stigma around hearing voices.
Idk, stigma exists everywhere.
Not always in the same ways, though that's changing as American cultural hegemony gets more and more ingrained.