An interesting thing about these comments is that, generally, they applied to all soldiers almost everywhere ever since the days of the Romans. Supposedly they carried everything with them on the march and their load was pretty much the same as an infantryman today. But some things change.
Typically, a highly theoretical marching load and battle load will be developed for the soldier. Then the worst possible thing happens: he goes to war. Right away theory is replaced by reality and it evolves. Reality is never static. Technology has always been changing and conditions vary, usually unexpectedly. Trench warfare in WWI was not something planned for years ahead of time, though other aspects of the war had long been thought about. The foot soldier was continuously handed one thing after another that he had to carry. Lighter weapons, lighter ammunition and lighter rations meant only that he could carry more stuff, not less weight. I'm not sure it's such a great idea to load everyone down so much, although that sometimes happens, at least to most foot soldiers.
Do you suppose the enemy carries around all that stuff, too?
Shoot low, sheriff. They're riding Shetlands!
Underneath the starry flag, civilize 'em with a Krag,
and return us to our own beloved homes!
Buy War Bonds.