Well, I'll revise my comments then. The rivet spacing on my '73 is the same as every other riveted seam in the trailer. Perhaps AS inceased the rivet spacing on window frames over the years because they were recognized as an issue.
I didn't find any more leaks around my window frames than anywhere else (which is not to say that I didn't have leaks). But, if you were seeing leaks with that large rivet spacing, then I could easily agree that by adding rivets you are fixing a problem, rather than just over-building it.