I think there's a difference between discrimination and not going out of your way to accommodate. I don't think you can discriminate accidentally, it must be intentional.
That being said, I don't know the legal precedent on this, I'm just talking from what I consider moral.
You shouldn't have to lower all of the shelves (or provide ladders) just because really short people exist, but if your employees refuse to assist when asked, then you have a problem. Likewise, Dominos will help blind people at their stores or over the phone, so there's still a way for them to reasonably order food from them.
I don't think Dominos should be forced to make their website accessible, though they certainly receive the negative press.