Safari and Chrome are absolute failures when it comes to exposing ARIA roles through MSAA. Accessibility isn't an afterthought at Mozilla. It's core to what we do. Apparently it's not even that at Google and Apple. At least Opera and IE are trying.
update: Building a fully-functional Web browser is not an easy task and building one that is accessible to everyone is that much more difficult. If Apple and Google don't care about users who require assistive technologies, that's a real shame.
From where I'm standing, it looks like they're not really even trying. Chrome gets a zero and Safari is only a tiny bit better. Maybe they're going to improve, but it tells you something about their priorities when users with disabilities don't make the cut for a 1.0 and a 4.0 release.