Originally Posted by andrewclaus

There should still be a recessed lip around the axle nuts to prevent a loose wheel from leaving the scene. (Remember the hit song, "You picked a fine time to leave me, loose wheel?")

Perhaps the dropout slots are perpendicular to the ground when installed in a standard angled head tube.

There is a legal requirement that bikes have some method of holding in a loosened wheel. The lips mentioned above are often referred to as "lawyer lips."