Yes. Before we knew how difficult it was I asked a local Apple Store if they would upgrade the RAM after purchase. They said they will do a RAM upgrade, but charge a labor fee PLUS the "full Apple price" of the new RAM modules, and the latter is much more than the price difference between RAM options when ordered initially (because the original option price is the net of the larger RAM minus the base 8K RAM). So you pay a much higher price for the additional RAM modules plus the labor. Apple will NOT upgrade the RAM with anyone else's RAM modules. They made that quite clear. They had not received pricing info yet on the labor or RAM modules at the time I asked.
Interestingly, I also called a local authorized Apple dealer/service provider and they refused to upgrade the Mini RAM regardless of whether you wanted to purchase the RAM yourself or if they bought it from Apple. Of course that was very early and that may have changed since then.