If you go into tactics, then the main reason for the weaker performance of the Me 109 probably was the weak bombers of the germans. I mean, the only planes capable of defending the He 111 or -even worse- Ju 78 was not the bombers themselves but their escorts. So, if the germans had paid more attention to heavy bombers (something that Göring fortunately did not understand), these could have take care for themselves longer and the escorts would have had time to watch their own back also.
I would agree with you F_alk, the Germans just followed different trains of thoughts with the British regarding the use of bombers after WWI. However, my point still stands, I have yet to see stats heavily favoring the 109 over the Spit. If you want to compare the Spit MK II vs the Bf-109 (the types that were used during the BoB), the MK II had speed and maneuverability over the 109 (though the 109 could outclimb the Spit).
