Originally Posted by
andrasz
This is not a difference between the -700/-800, it goes across the range. Boeing introduced blended winglets for NGs as BFE for -700 upwards (not the -600) sometime in the late 2000s, from thereon all aircraft coming off the line had a provisioned wing which allowed rapid installation (2 days as opposed to 3/4 days on a non-provsioned wing). Many more -700 were built before this modification, effective from L/N 1545 on the -700 and L/N 778 on the -800.
Again, I don't know details, but what I remember is that it was much cheaper and easier to retrofit the -800 with the blended winglets than it was the -700 due to 'structural differences'. I assumed that meant more than just gage thicknesses, but I could be wrong.
Then again, it must not have been that much more difficult, since I rarely see any 737NG without winglets.