I found some info at the Ford media website that may explain why we're having so many problems with the A/C and climate controls.

Quote from Ford: "A new climate control system utilizes a new scroll compressor and larger air ducts and vents for improved airflow. This increased capability will warm the cabin and defrost windows in two-thirds the time of the previous model’s system. "
http://media.ford.com/products/presskit_display.cfm?vehicle_id=1377&press_subsect ion_id=421&make_id=92

I hadn't realized that the compressor is a "new scroll compressor", but then again I'm not sure what was used before '07. But this could possibly explain why older Expedition owners aren't complaining about poor A/C performance at idle or low speeds. New isn't always better!