That is certainly true, I guess I needed to specifically call out that he actually does reply. And this has been a constant recurring "rediscovery" every few years that GabeN personally responds to that email.
That also wasn't the particular point I was even talking about. The point was that a previous dev would most likely still have connections inside Valve given how easy it is for outsiders. And that even if they had zero connections, again, it would be super easy to get a response.
This is all just speculation, but a relatively confident one.
It is a real thing. Very few people have identical ears on both sides of their head, and almost no one shares the same shape with another person. There's a few active implementations of this on truly wireless earbuds, but the latency makes it irrelevant for most things except music. Depending on just how unique the ear shape is, it can drastically change how things sound.
In no capacity should it be a paid feature in a game, though. In a more competitive game with a lot of value placed on audio like Escape From Tarkov, this would completely change the game and how it is played.
TLDR: Your ears are unique, and your brain spends your entire life from the moment your ears are hearing things, tuning to them.