I would just bring up two specific factors that relate to that:I am sure I will get a lot of disagree by saying this, but I'm going to say it anyways. I understand the range on the Tesla is an estimate, but 6 miles should be comforting enough to get 2 miles out of assuming the driver is not speeding and doing high speed accelerations.
1) That "6" miles is about 2 kWh. That's about 2-3% of the battery, which is expecting more precision in this than in most devices we use.
2) It's not just one battery. As was mentioned earlier, there are thousands of cells in it, and there can be a little bit of imbalance of the energy and voltage in them, where some are a bit lower. Lithium ion batteries suffer severe irreversible damage if they get actually drained to dead. They are shutting off the car just before this point where they would be killing some of the battery cells by overdraining them. So if they were to do this, to give people those extra few miles worth of energy when they really do need to be cutting off the pack, it would kill a few battery cells. And then the next time they did that, it would kill a few more. And you think people are worried about battery degradation now? This would be much faster, destroying small pieces of the battery at a time, before their useful life expectancy. And all that, just because people can't plan for some single digit amount of miles? They are helping you by not letting you destroy your battery.