That is not correct in that the car only charges when coasting. The system charges the battery but will decouple the alternator from the engine under acceleration or when the battery reaches 80%. If you are braking, coasting, etc. if the battery is not at 100%, it will then couple the alternator back into play.

Watch the video:
BMW EfficientDynamics : Brake Energy Regeneration

The bigger issue is that the battery is never getting fully charged. Short trips do not replace the amount of energy consumed by starting the vehicle. If you do a lot of short trips, BMW recommends that you either buy a battery charger or go for a long drive. If the alternator only worked when braking or coasting, then why would a long drive help? You could drive until you ran out of fuel and no power would have been put into the battery. The N63 issue is a little different. You have that the battery will probably only see 80% charge, but when you turn the engine off you still have the cooling system operating. Keep in mind that many manufacturers use a mechanically driven water pump; BMW is using electric. So how much energy is being used for the pump to run and how long is it running after the vehicle is off? You also have that after you open a door and get out, if you don't lock the vehicle, the radio is still operating. Once again, consuming power. Pathway lighting is also running. Then you have the normal items that are always drawing power; comfort access/remote receiver, etc. So even if the alternator only charges to 80%, you need to drive far enough to let the alternator charge the battery to 80%. If you only get it to say 75% on day 1, then 70% on day 2, then 65% on day three. You are not driving far enough to actually help. If you make a 5 mile trip and there were four stops, how could you ever actually charge the battery up? Especially if the cooling system is running the entire time.

Ford uses a different system so that a turbo timer isn't required. BMW doesn't use the same system as Ford but once again, they didn't want to use a turbo timer. Ford has battery issues of its own, it just may not to be the degree of BMW. Ford also isn't using electric water pumps, etc. A larger alternator might be beneficial for BMW to use. This way shorter trips when the battery is below 80% it can provide more power to charge the battery.