Interesting reading, thanks. So if I've got the gist right, it's the right to privacy that "drives" the law. Which is different to the UK.
So over here, if you want a badge that allows you to park in disabled parking spaces, or a travel pass that gets you a free career journey, then you first have to prove you have a qualifying disability. The easiest way is to show a letter saying "you qualify for this social benefit payment". No details of the actual disability. If you don't qualify for a payment, then it's much harder and you pretty much need to get your doctor to say "yeah, they need one because ...".
After that you then you fall under the anti- discrimination laws and so-on. But essentially the law says you first have to prove that you have a qualifying disability (including hidden ones) in order to get that protection / benefit available to someone with a disability. Then you have the privacy, in that you don't have to explain why.
Some travel brochures for Disney holidays will say that there is a DAS pass, and to bring along your proof of disability to show guest services.
I totally understand about hidden disabilities too, just in case the poster above interpreted my comment otherwise. DS has a hidden disability; it might qualify him for a DAS pass but we don't ever ask for one, just because we just don't think it's a necessity. But I know for others it would be essential. It was the process of getting one that confused me.