Well, first off, these cars weigh more than a Roadster and so need larger brakes to slow them down. A 911 Turbo weighs 1,000lbs more than a Roadster. An Aston DB9 weighs 1,500lbs more than a Roadster. Even a 458 Italia weighs 600lbs more. There is also a factor of design/looks. People think large rotors look faster - more like a race car. Same reason Model S has 21" wheels. Not very practical but they look cool. Also, this discussion is mostly about street driving. If you track your car you will have no problem keeping your rotors clean (the subject of the thread). Also in a track situation, larger calipers/rotors help to dissipate heat since there is more surface area both in the pad and rotor so lower temperatures. This keeps the brakes cooler and allows repeated hard stops coming into multiple corners per lap. So if Tesla, like Lotus, offered a "track brake system upgrade" then I would expect larger calipers and rotors. But if this brake upgrade is to solve the subject of this thread, the size of the rotors and calipers are adequate to lock up the wheels and therefore are large enough. We just need a rotor/pad combo that will have good initial bite even when seldom used.