@Chicken-meat
Well, being a moderator is a responsibility in itself. When there are countless of people on forums, you cannot expect them to treat everyone the same. Sometimes they aren't even abusive and rude, it's just how you perceive it!
However there are moderators who are genuinely abusive. There could be several reasons for this. One could be that they are awful people both online and in real life. Another reason may be that the fact that they have this “power”, the fact that they are important gets to their heads. Then they start being very rude and abusive without even noticing it. They think that this is how they are supposed to be.
I am definitely not saying that they are supposed to act like that. You should never be abusive to someone just because you're “more important”.