Yes, everybody, pedaling helps but the amount of extra range that affords depends on the speed, although more technically, the output power.
If you're going 20 mph, and you can pedal such that *without* a motor you can sustain 15 mph, you can greatly increase the range by pedaling. This is because pedaling would contribute more than half of the needed power to sustain 20 mph so you'd cut the battery-only power by over half.
If you're going 40 mph, and you normally pedal 15 mph unassisted, your increase in range from pedaling is practically nothing. This is because pedaling contributes less than 10%, and most likely less than 5%, of the needed output power.
If you're going 15 mph, and you can pedal normally going 15 mph, your "battery range" approaches infinity while pedaling. Who needs a motor?
So, like russell was saying, pseudo-motor-scooters don't really benefit much from this technique unless they really want to slow down, but "pedal pushers" can benefit a lot from it, depending on their desired speed and how much power they want to contribute. I'm already looking at a trip on my scooter that's about 20 miles in distance, and it's clear I'll have to go slower to make it, but if I were to take a bike, that range could extend significantly with pedal power. The only thing is that my bikes' ergonomics suck, so I'd get a recumbent for the trip (But that also introduces its own complications).