Naw, this is one of those often repeated ideas based on someone's guess being spread as a factual. Wounded troops don't actually cause more problems for a military than dead ones. Wounded can either return to combat after healing or return home to train other troops/work in factories/whatever. Dead troops means all the training that went into a person is now gone.

There's also the logistics of dealing with dead bodies, something much more resource intensive than people who are only wounded. Serious blow to morale if bodies aren't returned for funerals, nor can you leave them piled around because of disease.