Why are stock heights listed 5-1/4″ taller than the nominal wall height? (i.e. 8’5-1/4″ instead of 8′-0″)

WireCrafters lists the overall height of the partition, which includes a 3-1/4" sweep space beneath the wire partition panels, the 8' panel, and 2" post projection above the wire panels for a total height of 8'5-1/4".