I'm not sure what you mean by distributors. It would be the retailer who's responsible for not selling the prohibited games to minors, there would be no other restrictions on distribution of games. As far as the law being too vague, that could be the main reason the law is overturned. Basically every retailer would have to play every game and come up with a list of games that are unsuitable for minors. Of course, they could just take the shortcut of not selling any M-rated games to minors, but I don't think that holds water legally.
It's the retailer the one that also, gets penalized if they carry games forbidden by the bill and decides which games to sell. This in turn makes the publisher push for a certain kind of games; as usual the ones that sell the most. It basically turns the dreaded AO rating into an abstract concept that can be used to remove every "bad" game from distribution since the retailer can't be sure of what is what.
Hopefully it won't hold, but I would take Nepenthe's word over mine in that subject.