Actually, the 'trashcan' principle is used here, but only moderators can see posts in there. I can't comment on the 'slashdot' system; I haven't used it and it's not up to me anyway.
Whatever rules and guidelines exist for moderators (and they do exist), the interpretation will be down to the individual mod on the day. If he or she is feeling a bit less tolerant than usual, or there's been a run of PITA threads, patience may get thin and the moderation may be harsher than you might like. However, if you want absolute consistency then hire robots. People aren't like that - witness the controversies that very highly-paid international football referees get into over decisions that players and fans don't like. Why do you think we are likely to be any different?
Scroggs