Slingborg: If you look at the very first post Steve made a diagram of the signal the pedal sends, it is just two potentiometers - no fancy stuff. As I remember from Vocky's dismantling of the throttle body it is just a servo-type mechanism (a pot and a motor) with a spring to pull it back to the closed position if something goes wrong. Its all pretty low-tech.
A simple micro would do fine as you say - although it could be more fun implementing fast control for the OEM TB properly without making it hunt. RC servos might be a bit unreliable, but if you used one per TB on multiple TBs then if one fails on WOT its not really a big deal. You can buy industrial servos though, which IMO will be much better built than the GM one.
If you are feeding a TPS signal to the ECU, this can be faked from the micro. That means that even if the servo fails on the TB, the ECU still thinks the TB is closed so isn't putting fuel into the engine - it just adds another layer of safety.
Looking up the ST7 I can't see any real difference in features between the ST7 and a PIC - I'm interested why you reckon it is so much better?