It is very deliberate (like all of Charles' sartorial decisions). One of my favourite Charles photographs shows the pressed sleeve quite clearly.
At one time the practice was standard, even by commercial dry cleaners before automated pressing machines. It's of military derivation. The crease on the back of the sleeve also facilitates proper sleeve drape when hanging, and folding within luggage. Chuck's jacket sleeves have always been creased.
It's a practice apparently now as archaic as a neat vertical crease in one's shirt's collar - center back, which is the finishing touch to hand pressing a collar from the front edges backward. The process limits collar front wrinkling.
More details/discussion here - http://www.styleforum.net/t/135631/creases-in-jacket-sleeves-hrh-pow/0_50
Back in sunny (and too bloody hot) Melbourne now after a nice break, including a wonderful trip to Vietnam. I took a punt on the tailoring in Hoi An (which is, rightly, usually rated as not great quality or value for money) and got a unlined cotton M65 made up in navy based on this Boglioli one - http://linenforsummertweedforwinter.tumblr.com/post/21061082379/jhilla-boglioli-m-65-boglioli-knows-blue. Was a bit of fun and am happy with the result for the money.
Glad to be back in Australia, though not so glad to be back at work (surprising really?). Walking home yesterday I saw a middle aged man in a suit and flip flops which kind of sums up Australian menswear (with notable exceptions, including those here) and everything I love and hate about living here in one, hopefully not to be again, sartorial mess.