Whether a $2k laptop should or shouldn't have 16GB is a subjective opinion, so there is no way for me to argue that. My only interest is in arguing whether supporting arguments are factual and logical.
In my response to you, my meaning was that upgradability isn’t an important difference to the people in question unless they need more than 8GB. Sure, some will and it will be important to them, but if someone is buying an 8GB laptop, it doesn’t make sense to automatically assume they actually need/want more and would therefore find upgradability important. To use the car analogy, some people buy a car expecting to swap out the engine for an upgrade, but I’d say it’s safer to assume most buy a car at face value, so to them buying a car that’s easier to engine swap isn’t a selling point.
Sure, those are two examples of laptops that are upgradable. Apple may or may not be the only company that doesn’t offer upgradable laptops, I don’t know. But as far as upselling being the only motivation for companies to solder (as all companies do it nowadays), as I said, perhaps so, but I’d point out again that it’s also advantageous to the user because it allows for thinner lighter laptops, and some users value this.