Note true. Watch the power meter on the right side of the Driver Information Console while going down a hill in "D" mode - as you press the brake pedal you'll see the regen ramping up.my impression is that the brake pedal only slows using the brake pads. it does not cause any regen.
I did an unscientific test going down a long hill in "L" mode and then again in "D" mode. I couldn't notice any significant difference in regen power between the two as reported on the Driver Information Console. I suspect that the brake pedal will generate pretty much the same levels of regen as "L" mode does before engaging the hydraulic brakes.
In terms of efficiency, then, the main benefit of using "L" mode (aside from the fact that it's a very cool and intuitive way to drive) is that in "L" mode you know for sure that there is no hydraulic braking involved if you don't press the brake pedal. In "D" mode you might be wasting some momentum to friction braking if you hit the brake pedal a little too hard.