djs-
Cost is certainly always a production consideration for an automobile, but look at the two vehicles. Do you think the braking requirements are the SAME? The Mustang is a front engine car, the GT a mid/rear engined car. The weight transfer under braking is "likely" different. I am sure it is. So to say the GT500 brakes are puny compared to our GT's is just not a valid comparison. Apples and Oranges.
The "puny" looking rear mustang brakes have been discussed on other forums. But if you take the time to look at the 302S/R Ford factory race Mustang or other compttition only Mustangs where cost is of less importance you will see the same OE "puny" rear brakes. Why?
Because they are perfectly adequate for the overall vehicle braking required of the two rear wheels for this front brake biased vehicle. And I am sure the team development engineers and Ford Racing have reviewed this braking aspect and concluded the brake sizing is appropriate.