Originally posted by abhilegendProbably the most to the point answer!
He brings money to publishers. Wonder Woman doesn't.
But yeah, it's been mostly covered above. Flash may have a faster brain, but that can only help to a certain point when deduction and detective work are required. Flash is forensics, while Batman is forensics plus criminology plus psychology plus a host of other skills. He has the devious mind to understand other devious minds, the right amount of darkness to understand evil and the way criminals (and superbeings) think.
Strategy department? Bats has proven time and again that he can out think Wonder Woman and the others on the fly and come up with the winning play. Wonder Woman has great powers and skills, but no amount of training will make her as good as Batman in the other areas. And he is just as good at MA.
Green Lantern? Yeah his ring can do a lot, but I don't think it really provides applied knowledge. A lot of what Batman knows won't be found in a library.
Perhaps just as importantly Bats is the human element - and the JLA need that with all the other uber members. And to be in a team like that he needs to be damn good at everything he does. Sure Batman gets wanked by the writers sometimes, but so do Supes, WW and many others.