Measurement discrepancy on vfrmap dot com sectional -- is the grid wrong?
All the clues were there; another member figured it out (see comments).  My computer screen was stretching out the image in the left-right sense, so when I took my nautical miles scale off the tick marks on the north-south line of longitude, and then made an east-west measurement, the measurement ran significantly high.  The question noted I had seen this elsewhere and the fact that that was also on an east-west measurement, but at much lower latitude than Alaska (neither of which were noted in the question), should have been a clue to me as to what was going on.  Nothing to do with high latitudes and nothing to do with errors in the way the airspace or the map grid were charted.    

I looked at the same url on a different computer screen and the measurement came out fine.