I think you don't appreciate how clever the Fisker regen implementation is. It wouldn't be safe to generate .25G of deceleration through regen just by lifting off the accelerator, as it would be too abrupt and your brake lights wouldn't be on to warn the traffic behind you that you were slowing down that much. But while the Karma does provide regen while lifting off the accelerator, it generates additional energy by using regen (up to 90kW, as shown on an instantaneous digital display) to provide the first .25G of deceleration when the brake pedal (and brake lights) are actuated. This has nothing to do with mimicking ICE behavior, it is just a clever way to maximize regen without compromising safety or forcing a new driving style. I never suggested that the Model S be changed. My OP was seeking to understand why it behaved differently. Unfortunately, I still don't have an answer to that, although a couple of posters have suggested it may have to do with a difference in electric motor technology.