My cousin let me know about this thread so I signed up for TA to simply give my thoughts.
My answer to the op. I'm a Realtor in Austin and I specialize in new homes. The value I generate for my clients is that I usually spend 3-4 days a week specifically visiting builders and on site sales reps and pre-negotiating deals. Because of my relationship with the reps, quite a few will actually tell me their bottom line in addition to every credit or promotion I can get for a client before the client ever walks through the door. The fact that I can save my clients time and usually several thousand dollars more than what they can negotite makes up for my commission, plus some.
Also, no matter what they tell you, builders are not in the habit of rebating you a Realtor's commission if you are not represented. They would be in serious jeopardy of getting blackballed by Realtor's if they did.
Just my thoughts, have a great one.