All of you are correct about tipping and rates.
There are several points to consider and different reasons that may be good or not. Let me start off with the fact that I am not wealthy, in fact I am a working man. I enjoy a great massage and find them necessary for my well being.
I do not go out to a restaurant to eat unless I can tip reasonably. Do I tip for pis poor service? Yes, most of the time. People can have bad days, if you leave them nothing that confirms their bad day and attitude was appropriate in their eyes. I will often tip roughly 10% for piss poor service, it may help them to realize their poor service provided. Also being a local I don't want the rep of being a bad customer.
Now, back to the AMP's The ladies there often work for tips alone, the house usually gets the hourly rate for their expenses. The $20 dollars for mediocre service is reasonable IMO, plus you never know where some kindness will get you at an AMP. You have to get to know them to find out what may be available. I have on the rare occasion got up and left in the middle of a session that was WORTHLESS. One time in particular before the big bust I was in NMB at a place. I asked for 30 min they provided a FREE table shower before your massage. The TS was great and showed promise, but the massage room was shambles and the girl kept demanding from the start for 1 hour. She yelled back and forth to the house mother for a while, I got fed up and walked out. Boss said she would call police I said go ahead your sign says Free Table shower.
For an exceptional legit massage I have tipped 60, they appreciate it and try even harder the next time. Sometimes a couple $60 tip visits will eventually get you the secret handshake.
So for those looking only to get their rocks off, sorry I am contributing to the "problem" as you say. In the end it's all about me!