Circulated Vs Proof - Need Clarification

With proofs, it is a lot easier to get higher grade coins than with coins that are in circulation.

Because the coin produced for circulation are mass produced , that mean the mintage for this type of coins are extremely high ,When coins are minted they often bump into each other and receive small nicks and abrasion marks during the production process, in average the best grade you can find in rolls for circulation coin are between MS-60 and MS-63.So if you can get a hand on MS-64 or higher its a more rare and valuable.

As for Proof coins , I found a good description on Internet here it is:

By treating the die in a special way, the coins it produces have a different appearance. Modern technology allows the high points on the coin design to be acid treated (on the die). The background (field) design of the coin die is polished, resulting in a mirror-like look on the coin it strikes. This gives the finished coin a frosted look (frosting) on the raise parts of the design, with a mirror like finish on the background. This contrasting finish is often called "cameo". On some older coins a cameo appearance is quite rare. The attribute "CAM", when added to a coin's description, means cameo appearance. "DCAM" means deep cameo, and indicates the cameo appearance is strong and easy to observe.

Proof coins are struck twice, or more!
Not only are proofs made using specially treated dies, each coin is struck two or more times by the coin die. By striking it more than once the metal is forced into all the crevices of the die, thereby giving a very fine detail to the image on the coin. This fine detail does not appear on some non-proof coins.

Hope this will help you understand.

here the link of the information I've found : http://lynncoins.com/proofcoin_article.htm