I'm curious to know if you've actually confirmed any cases of people "abusing the system". Unless this is actually a problem, and was happening in more than one or two cases with the old system, this is somewhat reminiscent of premature optimisation. (And if it was in the Lounge, then you could just not allow rating at all in that forum).
I also don't really see how you can judge some users less likely to "abuse the system" than others. Letting everyone vote both up and down means that you end up with a post rating representative of the community as a whole.
Yes, many many confirmed cases. Put it this way, if there wasn't we wouldn't have bothered to address this as an issue. On judging users less likely to abuse the system, unfortunately what seems ideal doesn't always necessarily work out that way. If we didn't have to do this we wouldn't.
Right now we don't formally publish any guidelines as to how you become a moderator either, so this automatic selection of people with downvote capabilities represents something akin to selecting moderators. I remember how Slashdot used to call it Karma, and when you had enough Karma you would sometimes be selected as a meta-moderator.
