That is what I was thinking.
They seem to shoot wood arrows which ( I'm not an expert on wood arrows) I believe it would be harder to get in a real light weight. So they shoot a stronger bow to increase speed in trajectory for the different range shots.
My guess is if you were to shoot a really light carbon you could get away with the same thing with a really light bow, since your just punching holes and balloons.
You would might loose showmanship points though. It definitely more interesting to me to watch a guy shoot an arrow out of a bow capable of taking any game animal on the planet, and hit stuff I might miss with a 12 gauge!
Just some thoughts, love this stuff!