Yes, to their customers. With Getaround you need to go to a gas station and refill the car to a specified level (typically full) every trip, no exceptions ever, even if you only used it to move your groceries 10 blocks. OTOH, the hourly price is lower.

With Zipcar you must return the tank at least 1/3rd (maybe it's 1/4th) full, but there is a gas card in the visor. They're apparently using some kind of fleet management system, because the gas pump itself prompts you for the odometer value and your "driver ID" number (on your Zipcard) before fueling. Same interface at competing gas stations, so it's apparently a standard thing.

It's a bit unpleasant because you can't cut the reservation time too close to your needs - need to allow extra time to go to a gas station and back.

Totally, I'm always stuck with the Enterprise Car Share car with less than 1/4 tank and get stuck with an extra $25 'refueling fee' when I don't take it back (I have to pay for the extra 15 min of rental time PLUS stop by a gas station--which is super annoying). This would be a killer use case for their fleet to manage.

Sort of. Car2go gives you credits for refueling the car, for example.

Nice idea. I don't think they do