That isn't exactly all they pay. There is one more piece to the puzzle. All companies have another figure built into the price called "hold-back." This is the average amount of interest that a car accrues while on the lot. What they do is take an average of the interest lost when a car just sits on the lot. Some may sell the first day they get there and others may sit for a couple of months. Sometimes you can get them to go below invoice and take this "hold-back" out. On and STI it is no more than 800-900. But keep in mind this is averaged across all the cars on the lot.
As far as Mastro selling the 05's for cheap, they might have incentives that they are giving up from the factory, they could also have things like owner-loyalty or active military discounts. Most of the time the price is just to get you in the door. Most people don't qualify for these prices. What I have learned is that if it seems to good to be true, it normally is.

Take it or leave it guys, I 'm just trying to make you realistic.