Where does it state that RAM is user replaceable? Because computer companies allowed for this? Do you know how many RAM modules are improperly installed by the consumer? Do you know how many 3rd RAM modules are POS? Almost every computer I installed 3rd party RAM had problems about a year after I installed the memory.
Getting quality 3rd party memory and storage is difficult because a lot of it isn't passing the same tests that Apple requires. If you go to Kingston Memory site, they discuss how their memory is tested, which is consistent to Apple, as they are a certified RAM supplier, but the majority of the RAM that people buy is pure crap RAM that Apple wouldn't use.
But it's not just the quality of the RAM, it's the user's inability to comprehend that they need to wear a wrist strap, and these RAM modules are EASILY installed improperly.
You have to look at this from Apple's perspective. Why would they want a customer, that's typically not a trained service tech that's been trained using quality service parts can fix or upgrade these things? Would you want to sell a product that became more problematic when your customers start to do their own modifications to the unit? Remember, every time your customer screws up, it costs your company money to deal with the problem. You have to pay people to answer calls on issues that were caused by the customer and/or a 3rd party component that failed. These things have very slim margins as is.
Also, if what you are explaining were true, then the more expensive Mac Pros would be the systems Apple would prevent the incompetent end user from touching... Not the cheap, disposable Mac Mini.
This move is all about parting the Apple consumer from more of their money. Plain and simple.