The difference is that when one buys these cars, one can judge and decide for themselves if they like the UI and NOT BUY THE CAR if they don't like it. But once bought, the UI on every other car on the market does not change at the whim of the manufacturer. And yes, I've been vocal about the UI in my BMW, but no amount of feedback to BMW is going to change the car I currently own.
Some of us buy the car BECAUSE the UI can change. I for one think that it is awesome to get a new look-and-feel in an older car, not having to spend thousands of dollars to upgrade just for a newer looking and functioning software revision. Think about how angry people were because of AP was not able to be retrofit, because its hardware. I suspect there would be a much larger group of people complaining if V7 was only available on new cars (or models).
With software, you have the benefit of a very flexible platform...I applaud Tesla for continually looking to improve or modify the experience, it would be far easier to just let the UI get stale and focus on new models with new hardware.
Since we all learned how to drive and monitor our cars using the available information in the first place, I am betting we will be able to adapt and learn how to operate our cars reliably using the new layout and available information as well.