[dfox]

Requirements include thermal management (ie. cooling working in microgravity environment, without convection), power supply compatibility and EMC.

I assume that the thermal management part is significant reason for use of thinkpads. On another brands one can see that cooling is significantly dependent on orientation (usually with the best orientation for cooling being something other than "standing flat"), while thinkpads are able to get incredibly hot in any orientation, but I've never seen one overheat.

Another thing is the whole reliability and serviceability thing.