I believe Bla is right. We're slightly off center from the center of the galactic plane.
Try this... Hold out your hand flat in front of you so that you can only see the side of one finger. Now move your hand down slightly, so that your eyes are no longer perfectly inline with your hand. Notice how you can now see just the top edge of your other fingers. Making it look like there's more stuff slightly above your finger than below it.
Does that clear it up for you?