There are two points. One is that we're not forecasting, but rather assuming, the futures curve that was there at the time for energy prices, which is about a 10% decline, as you note, over the course of the projection period. As well, we do make a forecast for non-energy commodities, which over the projection period is about a 15% gradual decline from the levels going in.
All other things being equal, those factors would lower the rate of growth of the GDP deflator.