Why oh why, doesn't Google make it so that it reads your cookie and doesn't count it as a click? By the way I'm using www.asrep.com which also has anti-fraud alerts/prevention tools. E.g. you can tell it to not allow more than 5 clicks from the same IP on the same day, etc. Also I've been noticing that the duplicate number of clicks from same IP seem to not count in AdSense... so may be they already do that...
As far as I know, 90% (or 99%?) of the times, the reason isn't even click-fraud. But the poor employees at google got no other default templates to use, so I won't blame them at all.