Not forgetting of course that the 747 wing was designed back in the early 60's. It was just tarted up a bit for the 744 (grew a bit of span and a winglet!). The triple seven wing design probably got set in stone in the late 80's and being of a better design (supercritical?) there was no need for a winglet. Having said that, the next incarnation (read, falling sales!!) it will probably sprout a 'blended' winglet.
