That isn’t actually true. The price on the shelf is considered to be an invitation to treat. By taking the item to the checkout you are offering to buy it which they can reject. In practice they will sell it to you for the price on the shelf but this is not the law
We do. It’s called the Equality Act 2010. It requires reasonable adjustments for disabled people. However, this is not always provided for in reality. The equality act is mentioned in the original article