Yoda = Emperor.... Anakin=Obi wan.... The two fights (Anakin/Obi)(Yoda/Emperor) are a clear contrast of eachother... Anakin arrogantly persisted to keep fighting, resulting in a loss. Yoda retreating, forced a tie. I believe Lucas used these two fights to contrast the decisions of Jedi/Sith, and the repricutions of their decisions. Yoda's retreat is not a loss... to consider it a loss is totally unintelligent. If you have speculation against this, remember Russia's retreat tactic in WWII (Scorched Earth). Falling back to fight another day is in no way a loss, it is in fact a very well strategized battle technique.