It's only "simple economics" for people who don't understand the behind-the-scenes of how this thing works.
For non-Disney restaurants on the dining plan, Disney compensates the operating participants for the difference between the value of the dining credits paid and the menu price of items ordered. In other words, if a TS dining credit is "worth" $40 and you order a one-credit meal with a menu price of $43 at Rainforest Cafe, Disney makes up the $3 difference. The dining plan has no impact on non-Disney restaurants.