It's all a bit muddy, but as far as I understand it, the law does not disallow non-users to access Facebook.
I think it's like this: the privacy commission thinks (and I agree) that Facebook should not be allowed to track non-users: they have never agreed to it. Instead of stopping the tracking, Facebook denies access to non-users.
Also, that is not about all of the site, and certainly not about registration pages. IIRC it's about Facebook pages of companies, organisations, events and stuff. These days, it seems, there are quite a lot of organisations that don't have a proper website of their own, just a Facebook page (which is mostly pretty uninformative, but that's besides the point).