I think it's the mix. If you listen to the mono mix, John is only double tracked for a little of the mid 8 but nowhere else. This actually makes the song less untidy and doesn't detract from the lennon vocaL at all. Also, I think the drums may have had some revrb to make them sound more'live' in the stereo version, which isn't there on the mono. Worth listening to both as a comparrison.