Keep in mind that 0.1 g deceleration at low speed generates much less power than 0.1 g deceleration at high speed. High speeds means more power for the same torque. The car seems to have similar logic for acceleration as deceleration: constant torque/acceleration/deceleration 10 mph - 40 mph. constant power > 50 mph. It's possible that the motor can only handle so much reverse torque or reverse current at 20 mph, or it's possible that Tesla just thought users wouldn't want more than X deceleration force from the regen. Also, it might feel a bit weird if the deceleration force kept increasing as your speed kept decreasing. Anyway, as you say, the regen limit could be hardware or software, I'm just pointing out some possible reasons why the limits exist. - - - Updated - - - and for what it's worth... after you get used to it, I like that Tesla kept the pedals separate. Right pedal for electric acceleration/deceleration; Left pedal for friction brake. It's simple and it works.