Using the same illogic as Lincoln did in his speech, one can just as easily picture Cornwallis going back to England and writing the Americans a letter: "Hey George, remember that little thing at Yorktown where I handed you my sword and said I surrender? Well, funny thing is I thought about it and we decided we aren't gonna honor that any more. So would you mind giving my sword back? Oh, and the king just appointed a new governor to administer you just like the good old days."
Lousy example. Cornwallis' surrender didn't end the war. It just surrendered the British army. The war ended when the Treaty of Paris was signed.