A good and fair question James. I'm still ingesting my morning caffeine, so y'all forgive me if my answer contains errors.
As best as I remember, without digging through my books, the panels were screwed on. (They sure didn't use buttons, zippers, snaps, nor were they a press-fit as I recall.) They serve the purpose as their name implies: they are there to inspect the control cables and pulleys. As I see it, trying to see it from their perspective, anytime you have a cable making a ninety degree turn through a pulley, you run the risk of abrasion, wear and tear, etc. Understand, heavier-than-air aviation is less than twenty years old at this point, and some things are still being worked out.
- No, they aren't on all British a/c. However, look at a Sopwith 1 1/2 Strutter. Along the starboard side of the fuselage, you'll see lacing that runs up from the bottom and then back towards the tail along the side. As I understand it, this is to give the mechanics/fitters access to the fuselage to check and or repair the control cables. This is something unique to this particular a/c and as you noted, was not a universal feature. You can imagine what PITA it would be is an a/c returned from a sortie with a control cable severed from hostile fire, and you had to access it. How the Germans and French dealt with this, I do not know.
I know this doesn't fully answer your questions, but I hope it helps some.
Warren
