Scale and perks will drive that 5% up, I imagine. Sure, Joe Average can buy a Tesla Model A (for automatic, obviously) and have it operate as a AI-Uber Driver, but Uber can buy a fleet of thousands, allowing them better pricing, better access to charging stations, better data about which rides are most valuable and where to position their cars. With a bit better margins comes things like bottled water in the cars. This differentiates them further, etc.