I don't think it has to do with the fact that the DP costs $400....... it has to more with the fact that people still have to make car payments.......car insurance as well as whatever other bills they have (rent, ultility, phone).
and the $400 isn't exactly something someone has to just fart out there butt and drop on a DP.
I want a DP, but I'll have to save up for it..... along with the other mods I would like to put on my car..... My friend once went 2 months eating nothing but cup o noodles every day just to save money to buy a turbo he wanted for his RSX..... what does that tell you? LOL yeah that might be a little extreme, but not spending money on groceries enabled him to save up what he needed for the car....