Don't forget that nobody usually pays list for the average new car and that the available no-trade discount is normally included in the trade-in value offered by dealer.
For example, list $30k available for 28.5k with discount of 1.5k. Trade-in valued at 6k for net of 24k has really only gotten you 4.5k plus the tax advantage pointed out by SVTCANUK. Private sale usually nets more than trade-in especially when car is over 4 years old, but the time and effort to sell separately is not attractive to many.
