mpdmedia: Basically, I agree with you. Nevertheless, ancient coins get sold just like any other numismatic material.
The situation must come down in the end to "caveat emptor". In Real estate, otherwise translated as 'buyer beware'. The obvious proviso is that there is no attempt by the seller to deceive.
So it comes to grading, but dealers still have to sell their stock, so they are obliged to grade, especially if an item is not illustrated. This grading becomes part of the overall description of the coin.
It often comes down to eye appeal with ancients, and the buyer makes his decision realtive to the overall description and the price.
Personally I like to see all ancient coins in the hand before making a decision to buy, except that if the dealer has a top reputation such as Heritage.
I have bought Roman and Greek gold from top London dealers in this manner. These coins were negotiated beforehand with photographs. This is why you can buy from the top auction houses with confidence.