as D&P OR, and marcomo say, those are just the percentages of the demographics of coin-circulation, in the silver years (1964 and earlier). Unlike the ratios of dimes to quarters in your pocket right now, it seems that the dimes-to-quarters ratios in people's pockets then, was different. So for example if you were in a place prolific with easy clad right now, you might expect a certain # of dimes per each quarter you'd get. But for sites giving up older coins, it seems the dime ratio was higher. Go figure, a quarter bought a lot more back then !
Another factor might be that quarters are much more easily seen, when dropped, as opposed to dimes which are obscured in grass blades easier . Hence more likely to see the quarter you just dropped, versus a dime. This might hold some truth too, since I've seen how after beach storm erosion, when silver coins are showing up on the beach, the quarter ratio seems to be a little higher. Sand hides things much easier, so you could loose a quarter or a half , and immediately not see it when it hits dry fluffy sand.