It would be my assumption that the computer algorithm contained within the OEM module is optimized to a particular engine and transmission type so the throttle modulation is appropriate for each powerplant and axle gear. Aftermarket modules typically have adjustable sensitivity settings so the throttle position isn't moved to quickly or slowly with changes in speed and so the change in throttle position is appropriate (not too little or too much). Basically, higher power engines with deeper gears require far less sensitivity and the servo requires less delta appplied to maintain steady speed with changing load. A module for a lower power car with highway gearing would cause the muscle car to hunt. However this is less true with complex algorithms that monitor rate of change. Some folks may notice that Ford OEM cruise controls are inferior to most Chrysler of similar vintage. My '02 Taurus tends to fall asleep when entering an incline and then suddenly apply hard throttle to recover..it also overshoots at the crest of every hill with delayed throttle closing...while my similarly-underpowered '01 Dodge Caravan maintains perfect speed, smooth as glass.
Since OEM modules are fixed, so they are pretuned for certain hardware. this doesn't mean wiring differs.