K7JBQ:
Don't think it has changed. Usually, when I beat a higher-ranked player, my average goes down, but it's not always posted immediately.
Well, I might agree if your notion of "not always immediately" could expand into the "months" range ...
My average was about 65.xx and it lowered (in the past) to 64.00 thanks to MP wins over higher tier players. Now I am stuck at 64.00, no matter if I win against a TM or Legend (match play, ranked game, no forfeit, no concede except on putts).
There may be many explanations: you maybe should play for credit; or the improvements are saturated away after a certain score; or WGT took note that I am not spending money & black-listed my account ... I don't know. Anyway, my 2 cents of experience seem to be enough to argue that the "rule" is more complicated than the one proposed above.