Exactly. A vote 3 seconds after post is created/edited/voted-by-X is probably automated, the same comment on 100 posts as well. But there are auto-votes, trails, vote-selling, pretty clever comment bots...
Autovoters have varying response times as well, so detecting auto-votes would have to happen in ranges. Also not all trailers will always vote in the same order, so this would come down to detecting an unkown list of voters within a guessed range of time...
Stuff like this can certainly be detected somehow, but the complexity and computing time can grow pretty high pretty fast and I'm sure there will be false-positives in between.