When the Roman Empire was first expanding, regulators noticed an annoying problem: Due to increasing traffic, chariots were leaving grooves in the stone roads, but the gauge - the distance between the wheels - varied according to region. Different sized chariots didn't fit in the grooves. Julius Caesar had a solution: international standardization.
Changing every chariot to the same gauge was initially expensive, but once everyone could agree on the same standard, civilization was able to take a giant leap forward. More than 2,000 years later, the majority of the world's railroads still use the same Roman standard gauge. The actual distance of 4'-8 1/2" isn't as important as the concept that we can all agree on something.