I doubt very much that power is wasted running the electric motor against the friction brakes to provide the "creep".
The system is a control loop and the "creep" is electronically added at low/no speed depending on the position of the brake peddle. At some point the mechanical friction brakes are engaged and all power is removed from the motor. I'm sure that Nissan spent a considerable amount of time blending these things together and providing the "creep" of a automatic transmission car.
I personally wish they wouldn't have did this but it seems to make sense if you want the car to feel like a gas car.
One of the interesting things about good quality DC motors is that they use very little power while stopped, even if they are energized. I'm not saying Nissan *doesn't* turn off the motor while sitting stopped with the brakes engaged, but it wouldn't make a lot of difference if they didn't. You can check this yourself by taking your foot off the accelerator while climbing a steep hill. If the hill is steep enough, the Leaf will eventually roll backwards. (Good idea to check that no one is behind you before you try this!) Watching the energy screen, you'll see the power meter go to zero as you reach 0 MPH/KPH, then go into regen mode as you roll backwards!
That's right, regen is essentially the same as throwing the Leaf into reverse while moving forwards, and you can regen while moving backwards in D or Eco mode.
I would be interested to know all the same if anyone has been able to measure the actual power draw while sitting at a full stop in D/Eco versus N or P. I don't think the "Other Systems" meter is accurate. I think they have fixed settings for it based on which accessories are turned on, and don't measure this at all. If they did measure the DC/DC converter output, it would be very high while charging the 12v battery, then drop dramatically when the battery was fully topped up. They probably decided against that sort of reading, because they didn't want a lot of confused customers inquiring about it.
I have measured the draw from the 12v battery while in "On" mode (as opposed to ACC or "Ready"). This is similar to being stopped but without the traction battery engaged, so it's probably pretty close to the idle draw and it was around 8 amps with the fan, rear defogger, and headlights off -- about 100 watts. So, less than what the "Other Systems" meter reports by a factor of 2 or so.