babysilk, a lot of it is the "soccer mom" thought that the trucks get. Besides, how often do you see an Expy covered in mud? now, how often do you see and F-150 or Jeep covered in mud? I find my rig a very capable platform to play in the mud and whatnot with, even when it was completely stock.
Now, you start getting into the Gen 2 and Gen 3 Expys, that is a completely different world. I was part of a different group that one time got Ford involved just before they were to release the Gen 2 Expy's and Ford pitted the Gen2 against the Gen1's. There was like 50 Expys that went nose to tail through the woods. The only trucks to get stuck were the two Ford test mules (Gen2 trucks). The rear IRS does some funny things when out 4x4ing. Specifically, if you go over uneven terrain and push 1 wheel way up into the wheel well, on a Gen 1 Expy, this tends to lift the center of the truck up, which allows the differential to get past the problem. On a Gen 2 truck, when you do the same thing, the rear of the truck actually squats a little bit, making it that much easier to get hung up on something.