That is pretty descent detective work there!!
My genuine comment on this:
Is it possible that people think about getting karma on slashdot as a game? If you think of it as a game then you stop considering what impact your actions has on the discussion instead you try to cheat – because games has no consequences in the real work.
Cheating in games is also something we all grew up with (cheat codes in PC games etc.)
Anyways this is just a though