I don't know why Apple soldered the Mini RAM, especially seeing as it takes up about as much space as it would if it wasn't soldered. I mean, the AirPort card can be removed but not the RAM? Makes no sense.
On the other hand, there is no way they could ever try and keep every customer happy. The "tons of money" you mention would dwindle pretty quickly. I don't even think Apple could manage to make all the users on MacRumors happy- no matter how many billions they throw at the things people complain about here.
But yes, in the case of the Mac Mini, returning to removable RAM would be a simple solution to increasing goodwill.
It's very simple to keep people happy.
When you upgrade a machine, actually upgrade it.
Don't go backwards.
Come out with an OS that doesn't look like a 10 year old designed it.
Come out with an OS that is ready for prime time without major bugs.
OK, I'm sure even these things won't keep 100% of it's customers happy but at least they won't be pissed off