There are tons of situational factors involved. But, basically, fingers and body parts can't be near moving machinery. In this case, the sawa that LJ uses (At least in Methuen where I looked) don't have clamps and hold downs close enough to make the cut without the operator holding the moulding. A no-no. In fact, I beleive they should have active restraints, like straps to their wrist that pull their hands back when the blade comes down.
LJ used to cut less than 6". My guess is they hadn't been seen. Once they are written up for it, they better not get caught doing it again. Hence the restriction.
As for other vendors it could be either they have a clamping/hold down mechanism that allows them to cut inside 6", or more likely, they haven't been caught yet.
Theis is mostly educated guesswork, but it's probably pretty close.