That is true.... they are often purchased for use as passenger cars and not for their "intended" use as "light duty trucks". They are relatively cheap for such big vehicles because they don't have to conform to the same standards that cars do. In addition, they don't count towards CAFE, which controls how many fuel efficient vehicles of different sizes the car companies have to sell.
Even then, a fully decked out Expedition or Yukon can easily run into the mid-high 30's.
How much more would it cost if all the emissions, crash standards, gas guzzler taxes, etc, were tacked on to the cost of up-front ownership?