If the internal dimensions are that close, then the can count should be roughly the same. I don't know why the discrepancy, but perhaps how the cans are set in? I can say for certain that we actually did fit that number in the cooler. We did it the slow way--bought cans, bought bag ice, and loaded everything in the coolers by hand to get can capacity counts for every size. 128 cans plus ice was tight, but it's been done, and we have pics. We did take the cans out of the 6 pack rings and boxes (wouldn't want those on the river anyway) and so they nested together a little tighter.
Bottom line: both brands at that size hold a LOT of whatever you are wanting to haul.