I used to work for an industrial automation company, building custom-designed computers (the entire system, including the motherboard) that control manufacturin

I used to work for an industrial automation company, building custom-designed computers (the entire system, including the motherboard) that control manufacturing lines. The units we used to design, being field upgradeable, were far less reliable than the units where the memory and CPU were soldered to the motherboard. That wasn't an option for mass storage at the time. Vibration and heat do amazing things to components that are removable. Also, components that are soldered on the mainboard, by not using a socket, generate less heat. The interconnect can also be faster. So yes, upgradeability does tend to decrease reliability. By the time I left that company they had switched to entirely non-upgradeable units because they were far more reliable.