I always assumed that if you broke a SERVER rule while on cop, you would get banned accordingly. And that you'd get some type of "strike" on your APD record. After X amount of strikes in a given period, you'd be removed and blacklisted.
If you broke APD rules, then you wouldn't get banned, but you would accumulate "strikes", and depending on severity, you could be immediately removed and blacklisted. There should be exceptions though for breaking certain APD rules that would justify a server ban; such as giving away APD equipment to friends/associates.
I've felt this 2 part system has been fair.