pgyori - I also think you can get rid of the deliberately poor rounds if bad rounds aren't dropped. I can't think of a reason a player would shoot a deliberately poor round except in the circumstance where they are having a bad round, and then try to ensure that the bad round is bad enough not to impact their ratings (and even then, i would expect that the majority of players don't think/play that way).
The fact that we do drop bad rounds prevents the potential for deliberate behavior for Ams to tank rounds to drop their ratings to get into a lower division. The fundamental reason for ratings is to prevent sandbagging and get players playing the appropriate division for their skill level. Dropping bad rounds is a key mechanism to prevent any payoff from tanking behavior.