Stunning lack of historical fact and military history. The truth of the matter is Robb certainly had to impress upon his forces that this was NOT the decisive victory they'd marched south for. Polygot armies where each faction owed their allegience to their particular lord, not the overall commander were very wont to do exactly that. His reinforcing that there was still much to do was great generalship. It's part of the defining of the the Young Wolf as a military genius, on the battlefield. We all know what his weakness turned out to be.