I have no idea who votes for the winners, I imagine it to be a panel and voted on artistic merit not on what the public necessarily likes best. If that is how it's done, then the results would be arbitrary anyway so couldn't really be rigged.
The very fact that the studios & producers campaign beforehand shows it is political rather than each movie just being based on its merit. Wouldn't go so far as to say "rigged" but a little suss definitely. I'm sure not all of the Academy would be swayed by the campaigning. I guess we'll never really know.
Was suss when our Cate Blanchett missed out on Best Actress for film 'Elizabeth'. If ever someone should've got an Oscar in a role, this was it!
P.S. That was Daniel Craig's first film. He played the treacherous priest tortured by Walsingham, played by our Geoff Rush......