A brake pedal rubber that has worn through is a safety item. The driver's foot can slip off a wet, worn pedal in an emergency stop, and the pad is inexpensive to replace.
Accelerator pedal assemblies on drive-by-wire vehicles contain the pedal position sensor. Those assemblies are matched to the engine and usually require a relearn or a calibration after replacement, so the part number has to match exactly.
Pedal boxes and bushings wear and produce a click or a sideways movement. That play is felt as a vague pedal and is often blamed on the hydraulics.
