Also, part of it is that many more different people are grading higher and higher volumes of coins. Only a few folks previously sent to ANACS. More recently a lot of people are doing it, and seeing peoples success, even more are doing it (yes Nubbins, may not be accidental). With higher volumes, you would expect seeing more at the higher end ... but proportionately it would be the same .... if everything else was consistent
My current theory is that as people receive coins that get a high grade back from ANACS they are going to be more likely to be willing to sell it due to the high premium associated with the high grades, then they would with a lower grade, even if they want the coin to be part of their collection. I am just throwing numbers out there, however it would be possible that 100% of MS68 casascius coins get put up for sale right away, while only 40% of MS67s will be put up for sale, and maybe 30% of MS66 or lower. It is also possible that someone who receives a lower grade might intend to sell their coin only when there are no other similarly graded coins out there for sale.
If ANACS had an increase of 500% in the number of coins being sent to them over a certain time then you would expect a 500% increase in the number of MS68 coins being put up for sale, but maybe not for the number of MS67 coins.
If ANACS is giving out grades that it shouldn't be giving out (temporarily), then any potential buyer can be rest assured that they will be protected because ANACS guarantees the grade of the coins they grade, and will buy the coin back from you in the event that they are incorrect (and/or will pay you the difference in value of what grade the coin should have actually received). How they value these coins, I am unsure, and it would be an even larger gray area considering that these physical coins are almost always priced in terms of bitcoin.
I do personally think this is a very nice coin, and although I am no expert, I would certainly agree that it is deserving a MS68 grade!