The clear pane is on the bottom just so you can see the trailer. Whether that is a good reason or not depends on your use. For me, I tow a trailer which cannot be seen in the side mirrors at all, but can be seen in the rear view through the pickup window, the dual pane camper front window, and the door lower clear pane. Without that if the trailer parted company I wouldn't know until the next rest stop.....
My camper (BF 10.4) came with an insulated cover that snaps over the lower pane when it is not needed for visibility. If you never tow, then a door without the lower pane at all would be preferable.