It is deterministic, no ? Do they have some entropy source they use?
Maybe it's chaotic like you and me, but it cant be non deterministic, it'd mean it doesnt even really answer questions and just spout random tidbits :s
They use a rand() function as part of the input. I don’t think they have a source of true randomness they use, but it’s random enough for any practical purpose.
"Top StackOverflow expert on XX", so the incentive is still there.
One solution to spam could be to keep the voting system, but not publicly reward users with points (like on HN).