

Yes, after all other servers need this information in order to prevent double voting, you can’t just have servers sending each other information “somebody upvoted this” and also tell when servers are allowing users to vote more than once.
So upvotes and downvotes aren’t actually private, never have been, some servers may display them publicly even if most don’t.
Yes, but then you can have malicious servers sending fake numbers without other server operators being able to check whether this is at all plausible.
(It’s still possible for malicious servers to send fake votes, but server operators can see which users they are stated to originate from, then block that server if that looks like it’s doing that. At least that is my understanding.)