Just as an observation this was the first flight of the day. Normally I have found that this would mean the Captain flying as he would like to be the first to control the aircraft on the first flight of the day. This would mean the First Officer would do the walkaround check. The Captain signs for the aircraft on the say so of the Engineer and the exterior check done by the First Officer. These are highly reliable aircraft and the F/O may well not be as vigilant as he might be first thing in the morning. Just a thought.