1 thing I've learned is the quality and grade of meat available makes a difference.
I'm sure he's using a C.A.B for his brisket.
I also know he mentions S&P as his seasoning but rest assure he's using more than just that, and as any bbq person does, they will not reveal their secret to you.
Now I'm not saying his bbq isn't great, but hype, quality of meat, consistent cooking and spending years refining your craft all play a part.
I've had his brisket and it is DAMN GOOD, but I like the bbq at Salt Lick better so it's just a matter of peoples taste and if his bbq caters to the peoples taste in Austin then good for him.
Surprising thing is how many people in line are from out of town and come to try his bbq because they heard about it. I know that was why I got some.