If I have time I'll have to check but what I've paraphrased above is from our current Ops manual.
I think the aviation law is written bearing in mind that there's obviously two sides to this, it's not just the diasabled pax, there are the rights etc of other passengers and crew.
For example what if the individual's disability might impend others evacuating? Would the law demand that the Cabin crew to provide direct help to the individual in the event of an evacuation (and possibly risk there own lives doing so?)