I think there's been a push for higher tips from more shops and girls particularly in the chinese massage shops over the past year or so. However talking to the mamasans I know over a long period, there's always been some punters that tip a bit extra (and some that try to tip less!).
To answer your question, I guess the more punters that pay higher tips the girls get a higher expectation. Services have stayed pretty much the same as far as I can see. As has been said before the way the majority of punters behave will decide. Nothing wrong with the prices going up a few percent every now and then (everything else does). Once it goes beyond 'a few percent' punters might try different services, punt less often etc- we might be seeing a bit of this now.
Unfortunately we won't get any ABS statistics on this , so we can only gauge forum members' feedback.
P.S Good topic!