No it's not. It makes no sense to say "oh, you can't commute to work and then home again five times a week? so how do you get groceries?" because those are two completely separate things in completely separate environments.
It's none of Amazon's business how people manage their disabilities outside of work. The only thing that matters is what the most effective way of managing their disabilities is inside of work. Amazon is not your doctor, and if your doctor says that this is the most effective way for you to manage things while being productive then they need to accept that the doctor knows what they're doing.
If a guy asks for a special chair because they've got an injury? I probably ought to check whether they're OK standing for long periods, whether they're OK with carrying heavy things, whether they're able to self-evacuate in a fire, etc.
They are allowed to ask for medical documentation on what your limitations are.