The difference between the Aulani standard Annual Dues amount and the subsidized Annual Dues amount should actually increase over time. As you can see from
this chart on Aulani's Annual Dues amounts, the difference has increased from $1.42 in 2011 to $1.69 in 2016.
I can't say for certain how
DVC computes the subsidized amount each year, but it appears that each year the standard Annual Dues amount and the subsidized amount change by the exact same percentage. So, if the standard Annual Dues go up by 4% in 2017, the subsidized Annual Dues amount will also increase by 4%. But since the subsidized dues is a smaller amount to begin with, the actual increase in the subsidized amount will be smaller relative to the standard amount.