Washington understood. He got it. Although it took a few years until the way things worked settled in, he realized, as did all the founding fathers (and yes over much heated debate) that the commander of the army or armed forces was the President and he was/is a civilian.
We've had military men in the White House - and they have been good if not great presidents. One reason, and I'm just supposin' here is that they have a certain discipline born of service and training and by God when I give an order I expect it t be carried out soldier mentality.
McChrystal isn't going because he is a bad general officer. On the contrary, he is a tightly wound spring of an officer, who, like many of us, let's it slip now and then. If you were a special forces grunt in some hell-hole in Afghaistan you can wound up like a 7 day clock too but you CAN'T ever once let it slip...because you make it unsafe for everyone else Most certainly if the officer in charge says "do this" you "do that". period. no arguments. end of story.
General McChrystal seems to have forgotten that even he is to salute his commander and chief and when given an order has two choices: 1. do it or 2. resign his commission. He has no 3rd option which is to directly or indirectly call the commander in chief, his direct boss, anything other than "sir".
Don't let the doorknob hit you in ass when the door slams shut.