I agree, the umpires should be consistent, but we know they aren't. Some of it is a judgement call and sometimes they get it wrong. Everyone has their job to do. Players do not have time to call their own lines, make sure the match is officiated properly and worry about their opponent. These are the pros, where everything is supposed to be done for you. All you need to do is play. By the way, what Nads did wasn't necessary. He took it upon himself to award his opponent a first serve. That was a judgement call by the umpire.
P.S. I'm not saying the doubs team shouldn't have been DQ. I'm saying it was the umpire's job to do it, period.