Its just a hunch- but based on months of casual observations. Last year I was comfortably leading a poll and then suddenly got behind in quite a short amount of time. When it was level pegging and I got a vote within the hour there would be another vote to the other bike around 2 minutes after a new user had been registered. Coincidence?? maybe but it happened a dozen or so times. The names were similar- one word, three syllables, no location, no follow up posts etc. I became very suspicious and spent far too long watching the pattern emerge (It was whilst doing this that I spotted the ruse with the clone usernames- JeRkY. .orange71 etc that was flagged up the other week- its a common used forum scam used to defraud). I just accepted it and said nothing- its no big deal, I already have the T-shirt.
BoTM is supposed to be fun and not taken seriously but the standard has got so high that some people are spending big bucks to chase the win. Its a shame that the votes are being manipulated in such a way as to change outcomes. I'm not for a minute suggesting that the owners themselves are doing this- like you said, there are other national forums that might want to give a nominee a leg up, I don't know, but for whatever reason some people are up to no good.
I guess one way of doing it is for everyone who votes should be made to leave a comment of who and why they voted- that way if a bike gets a dozen votes and comments from users with just a few posts on a recently opened account, IP addresses can be checked by a mod and further investigations can be made. BoTM is a serious competition these days and there needs to be more scrutiny IMO.
Si