You're right, the glass is too tall, but I do not think the situation has much to do with the curvature of the door. Keep in mind that there is at least 2" of glass below the belt line when the window is up all the way, where the regulator attaches to the glass. The window is just too tall to hide in the door. Now this has definitely been over-analyzed.The HACK said:You guys are putting WAY too much analysis.
Take a look at the curvature of the window. Then take a close look at the curvature of the door. The window is simply too TALL to completely disappear into the door, since it has to go down in a straight path following nearly the same angle. To completely hide the window the glass would have to extrude past the door frame, or the window regulators would have to be microns thick.
EDIT: Image may not be ideal, since it's not taken of the door ajar STRAIGHT ON, so the perspectives are a bit messed up, but this should illustrate my point.