Supply Units Losing Vehicles

[Steel God]

While motorized infantry and motorized-drawn artillery are not vehicle units per se, their trucks and limbers are immune to the break down rule.

Because those units are counted in men and guns respectively, which for game purposes are immune from breakdown. If you included them you'd have situations where you have more men then could fit into vehicles, and more guns than tractors could tow, and while that all sounds very attractive to a realism nut like myself, from the game design point of view it's simply extra programming and extra complication to the rules for no appreciable change in game play.