Chances are you would have the phone at the side of you, e.g. in a pocket, so I think it's so that the shorter lead one is in the ear on that side.
Mine are the same, the left ear plug goes directly in the ear, and the right one goes around your neck and then into the ear- i might be wrong though!
That's what I thought, but mine (nokia music xpress) has one that is bloody ridiculously short. If it was to go in a pocket it would have to be a top one lol
