I've never done anything beyond amateur electronics, so sorry if I'm way off base here, but it at least seems intuitively plausible to me that soldering the components to the board allows them to work reliably at lower power. With a pin and socket connection, you've got to try and be at least reasonably resistant to corrosion or other sources of less-than-perfect connection.

That said, I don't know that RAM chips are the hill I want to die on, anyway. Could we get to a better place if we dispensed with the whole, "just the one big motherboard," design, and looked to the old backplane-style physical layouts? Then you could have a module that contains the CPU and RAM and suchlike all in a single package, and move other things that may not want to be quite as tightly integrated off to another package.