I believe katman nailed it. Tournament archers need shafts which are extremely consistent as measured out to 60 yards. They will pay (or get paid) to use anything they believe will give them an advantage.
Why is one basketball shoe so much better than any other?
I think it's pretty much the same whether you are talking golf, tennis, archery or claybird shooting. The guys who make a living doing that sport will definitely have a preference. Let's face it. Most of the games are mental games at the top level where your competitors are pretty much at the same development of skill. If you think something will give you an advantage, it probably will.
I've had a lot of people tell me the arrow is far more important than the bow, but at my level (and I don't think I'm alone) GT blems shoot more consistently than I do. When I get to the point I can sort out my matched arrows from those slightly different, group after group, I'll raid the bank for better (and more expensive) arrows.