Damn. The iMac used to be good enough for the pros. There's no excuse for soldered RAM in a desktop computer.
"OWC has ... learned that the memory is soldered in, which means it can't be upgraded...The maximum amount of RAM for the 21.5-inch iMac models is 16GB. "
And? This is for the 21 inch model.
The 27 inch model is user replaceable up to 64gb, pros would never use the 21 inch model which are then entry level machines.