We (Australia) moved to the USGA handicapping system - well hybrid system anyway - at the beginning of 2010.
Apparently this was done to simplify "things", enable electronic delivery and save costs of administering the previous handicap system.
Anyway it was determined that all our courses had to be rated with a slope index (never used previously) which would take considerable amount of time.
In the interim our courses were rated based on difficulty (isn't that the same as slope?)and that is the current basis of your daily result 72(score) - 72(rating) = 0 so you played to 0 when you shot 72 and from there it is your best 8 scores from last 20 rounds .. with the 20th round always replaced by the most recent.
Understand this is basically how your sytem works as well with our rating replaced by the slope rating ... but not entirley sure?
So .. after this was introduced many mid to low dropped a shot or two and high seemed to add a shot or two which was the exact opposite of the effect desired .. I think.
Anyway now it's vitually impossible to win anything playing on mid to low single figures unless you absolutely shoot the lights out .. but ... there are now alot more scratch 1, 2 handicapped golfers over here than there were before.
So back to point .. this system allows a dramatic drop if you have a period where you string some really good rounds together.