Actually in the US, the Americans with Disabilities Act does cover things like accessibility in a store. Equal Rights and all that ya know, this includes those that are disabled or "other" abled.
GameStop is a rip off, but if you take your games and agree to sell them, nothing you can complain about. You agreed, therefore it is a contract. Don't sell 'em if you don't like what is offered. I have stopped using Game Stop completely because they are a complete rip when it comes to what they offer as opposed to what their markup is.
and as far as "being in a wheelchair or a large person" a disability that is certified, is a disability, period. There is no distinction. The law must be abided and a complaint can/should be filed with the BBB at the very least, or a legal action could be taken if you were so inclined.