I think your faith in this "myriad of other laws" is somewhat unwarranted. Especially since this particular brand of law is pretty new, so assuming there's a precedent that they'll be struck down isn't really accurate. If you've got examples, fine. The best chance is that the ESA will force them to prove casuality. And it's not a great chance.
And this bill has many problems which could impact outside of "johnny can't play doom", as I list on my blog. For one thing, it lists violent games as harmful to minors and a potential cause of violence. This is precisely what guys like Jack Thompson need to start winning cases against Rockstar. The bill legislates casuality that science has yet to prove.
And then of course, there's this little thing called the Internet. If you were a small developer and trying to sell your game online, you're going to have to start thinking twice about it next week - because if you sell to some kid in Illinois you might get a lawsuit on your doorstep.
Mostly though, this bill shows that gamers need to be a bit more political. I know that sounds nasty and it might require a cold shower afterwards, but the Illinois Assembly walked all over anyone opposing this bill by threatening to flyer them to death saying they support violent behavior in kids. Who was there to raise an opposition? Nobody but crickets.