Grading has always been subjective and arguable, even 100 years ago. Back about 1980, Tulving, PCGS, and several other well known firms each had problems with the Federal Trade Commission over grading and investing. They are all in business today because they all signed statements for Federal courts promising not to sell coins as investments and also to agree that grading is subjective.
Generally speaking, grading reflects rarity. Coins are made to circulate. Therefore, less circulated examples are less common than those with more wear.
Obvious by inspection is the fact that the item with the lesser wear shows the greater detail. That artistic image is one of the reasons why we desire the object. If you randomly removed 1/3 of the Mona Lisa, what would you have? What if you just removed the "high spots" from
The Last Supper or
Marilyn Monroe -- or for that matter,
one-third of the pixels from your CD of your favorite movie? Obviously, grade matters.
... but it only matters so much.
It matters a whole lot with American coins because they are machine struck clones, each identical to the next, essentially undifferentiable, just a commodity like hog bellies or #2 Heating Oil: one batch is just like the next.
I have items that are virtual museum pieces: unique. I am not alone in that. I learned by reading Frank Robinson's
Confessions of a Numismatic Fanatic that if you study and specialize and specialize and study, you can own material more rare than a Brasher Doubloon. At that level, it would be nice if the coin (or whatever) were pristine, but, heck, just that it exists at all is amazing.
Here is the famous Nike of Olympia.
http://www.sikyon.com/Olympia/Art/olymp_eg08.htmlThis is the statue that Augustus Saint Gaudens copied his Victory from. Too bad that it is not complete. Would you say that it is not worth anything because it is not Mint State? Heck, it is not even an AU Slider. It might be a Good... Grade it as you will, it is Stunning.