Something's puzzling me.

Why does the GPA's door shutline cut into the windscreen pillar and part of the roof?

Not exactly critical to medical science, I grant you, but I was puzzling over it while washing bird crap off it earlier. 

Surely it's more expensive to engineer that way.  It doesn't reduce wind noise, or improve the weather seal*, and I can't see that it can be to improve headroom, since there's tons already.

I thought maybe it's to prevent the doors from jamming in a crash, but the 500 has a conventional shutline, so it's probably not that.

Any ideas?

(* incidentally, I think when Tom Ford complained that his test car leaked, he actually meant there were a couple of drops left on the rubber seal from when he opened the door.  The water on the roof always pours in when I get in the car.)

It drops into the boot when you open that as well.