Can SCVs/Drones/Probes carry different amounts of resources?
I have a few theories on this one. In Warcraft, there was a section of the EXE which had the values in it for the amount of resources that one peon or peasant could carry, and the various upgrade values. So one theory would suggest that these values are in the EXE somewhere. Another theory would suggest that the values for the amount of minerals and gas they can carry are in the Units.dat file somewhere. There are many variables in there that have an unknown use, and one of them very well could be the amount of resources carried.