@SixZeroFour - Pat Pending also and looks like it has rubber treads. Does it have plastic wheels or metal wheels? I wonder if your Mediterranean is the same year as my Eastener and Weber was experimenting that year with this style of lid?
I don't really know offhand, but is the vent and the area directly underneath the vent normally flat or curved? Maybe this was just an attempt to make the vents seal better and/or easier. Matching two flat surfaces would seem to be easier than getting two curved surfaces to match. Even if that worked, someone may have decided the appearance or process to make flat area was not worth the improvement in function.