I think this has to do with the higher revving tendencies of the mach motors. A friend of mine just wasted his engine due to a failed oil pump on an NA cammed GT, so this would support this theory.
They've got a red '05 GT (auto) at the N.Aurora Auto Mall at 88&Orchard. Swung by and sat in it but they wouldn't let me take it out... something about it not bein ready to be test driven?
Ah well, I wouldn't buy an Auto anyways...