Timing retard

I have heard the term :"pull out dwell", associated with FOB ignition. But like nearly any single coil ignition, at high RPM, dwell time decreases.

I was aware of that as well. But when Don at FBO specifically told me that all transistorized ignitions retard timing during high load, it got me wondering. I thought all ignition control boxes were basically just a switch telling the coil when to fire. How would it know when the engine is under load? I realize Don is in the business to sell ignition boxes, but is there any truth to his claims?