However...I did end up going to another dealership that didn't do the adjustments. Since I tend to stick with vendors, especially for large ticket items, I suspect the total lifetime value the first dealership missed out on by tacking on the market adjustment (that they didn't tell us about until we asked -- it wasn't on the sticker), eclipses the extra profit they would have made on that sale, even when adjusting for the time value of money.
If you are beneficially affected by price changes, then price changes are a result of supply and demand.