Excellent point Egorvlad - in bypassing the Hornburg to destroy Edoras, Saruman would have left his forces vulnerable to a counter-attack from behind with a better organized Rohirric force. And you have to ask yourself the question: would you rather have the decisive battle of the war for Rohan fought on the plains somewhere with the decided advantage that Rohan's cavalry provides at that point, or engage in a siege battle with a smaller enemy force holed up in a keep? I don't think Saruman chose his strategy poorly in this regard. If he had won the battle at HD, it likely would have been the knockout punch for Rohan.
Originally Posted by Egorvlad
"I do not love the bright sword for its sharpness, nor the arrow for its swiftness, nor the warrior for his glory. I love only that which they defend," Faramir in TTT by JRRT.