With a short sale you are trying to convince a lien holder to let go of a property for less than what is owed on the property. This takes much negotiation. Not only that, but like some of the other answers say, it can take a very long time to close on a short sale. You run into resistance from Real Estate Agents (like you've encountered) and also by Mortgage Brokers/Banks that want nothing to do with these types of properties. I have recently had, even in this economy where you would think somebody would jump at the chance, Mortgage Brokers tell my clients that a short sale was too much work and refused to work on one.
To answer your question, YES. There are definitely agents better at short sales than others. They will have experience in selling previous short sales (you may try and find some recently sold short sales in your area and contact the selling agent). A lot of them will have extra, specialized training on short sales. They will have greater negotiation skills. They will also have a network of people to assist in the short sale (including lenders willing to lend money on short sales).
You are absolutely right that this is a good way to find a great deal, but may not be the best for many of these reasons. There are other pre-foreclosure deals out there, but are harder to find. When the seller owes less than what is owed there is more of a chance to get the home for less than market value.