Good design also means using less materials, and it's obvious that soldered RAM would not need the plastic socket. If only 10% of Mac mini owners upgrade their RAM, then that's 90% of wasted sockets out in the world.
I, too, wish Apple would design their systems to be more user serviceable, but there also needs to be a realistic balance stricken. Apple is probably well aware of roughly how many Mac mini owners would perform a RAM upgrade. With the Mac minis coming with 8GB out of the box, that will be more than enough for the vast majority of users, and for those that need more, they still have the OPTION of getting double that amount at time of purchase.
Pressure on Apple is always a good thing, so I'm glad to see this issue discussed in such depth. Let's hope that Apple is paying attention.