So you have the ability to discern the difference between MS63 & MS64 but not MS67 & MS68. That does not preclude others from having that ability and it does not mean there shouldn't be a price difference between the two grades. Your other arguments are counterintuitive. If the graders don't have the ability to be consistent, why would it be necessary to resubmit a coin 10 to 15 times. The use of population reports is a guide to the conditional rarity of a coin. Everyone knows they are not completely accurate. That does not mean they are completely useless. In the example given, the 1944-D MS67/68 FB Mercury Dime, you would have to be a fool not to believe that the number of 67's is many multiples (15x-20x) that of the number of 68's. For someone who can't discern the difference between two grades, you are right, it would be silly to pay more money. For those that can discern the difference, the price variation is warranted and expected. And I agree that most casual collectors don't know the difference. On the other hand, most of the graders at NGC and PCGS do know the difference.
Here's the thing as I see it - people don't really understand what condition rarity is until you point it out to them. Most of the time, when condition rarity is mentioned people automatically theink you are talking about modern or semi-modern coins like the Mercs you refer to. But condition rairity exist in all coins, not just the new ones. Condition rarity is a real and tangible thing - and it always has been. It's just that nobody ever seemed to talk about it until high prices began being paid for what people consider to be common coins - like those Mercs. But consider - Morgan dollars are just as common as those Mercs, and maybe even more common. But nobody bats an eye if a 6 figure price is paid for an MS68 Morgan. Same for a high grade 1909-S VDB Lincoln - and they are so common I can find you 6 of them for sale in a few hours. But nobody says - oh it's just a condition rarity, those coins aren't really worth that much. No, what they do is go - WOW an MS68 Morgan !!! Or an MS67 S VDB !! Their eyes pop out of their heads and there is nothing but ooooohs and aaaaaaahs. But when it comes right down to it, that 68 Merc probably is more rare than either of the others. But because it is a semi-modern coin it is spoken of with disdain. Now don't get me wrong, you and I think more alike than you might think right now. When it comes to rare, I don't even consider something rare unless there are less than 10 of them in existence. But I was just trying to point out, and not just to you, that condition rarity is not what most people think it is. Condition rarity applies to all coins from the oldest ancient to those coming off the presses right now as I type this. Who gave them the right ? We did. And we is the collectors and dealers in this hobby. We gave it to them when "we" decided to accept what they were turning out. We gave it to them when we flocked to them in droves the very first year they opened the doors - begging them to grade our coins and waiting 4, 5 or 6 months just to get them back. And then "we" continued to send out coins to them in unheard of numbers, ever increasing numbers. And it hasn't stopped. I wrote my first article about that almost 10 years ago So far, nobody, or very dang few, has been willing to listen. The crack about the eye doctor was made in jest. Well, as you know, it's easy to misjudge someone's tone in a post. Reckon I misjudged yours. Hopefully, you also realize by now that when I respond to a post I am seldom just responding to the previous poster. Most of the time what I write is written more for the others that will read my words than it is for the person I am responding to. But you asked what I took to be an honest, and valid, question - so I responded.