This is generally done to protect battery cell health. Much like SSD memory one cell in the battery failing will ruin an otherwise fine battery.

Yes, many electric cars have a buffer. Not all Tesla though. That's why it's not recommended to charge a Tesla to 100% everyday while it's fine with many other brands.

But Tesla did sell a few cars with different battery capacities and exactly the same hardware. If you got the smaller capacity then you got a buffer. Tesla could unlock the buffer remotely, if you give them more money or if you need to evacuate before an incoming hurricane or similar.

Yeah I think fair to charge the customer more to access more of the total battery capacity because Tesla is now assuming more warranty risk on the battery.

Was gonna give the same example. It’s common industry practice sadly. Tesla and gopro are hardly the only two offenders. It used to be a common tactic among cpu manufacturers also.

What is the problem? You get what you paid for. A lot of costs are R&D. If they wouldn't do this they most likely wouldn't sell at this many price ranges.

Can you hack your battery to use its full capacity?

It is unclear if anyone has broken through the crypto on the battery pack firmware (at least for newer cars, Model 3 and Model Y). Similar for the motor controller firmware.