Who is responsible for discounts?

This whole topic started with a post where a customer forgot to ask for their discount, and retroactively requested it before their stay was up. I do agree that it is the customers job to ask for discounts they qualify for after seeing a list of those posted at the business or their website. But the rub begins when a customer is aware of those discounts, but forgets to ask for them. I have done this several times in making camping reservations where I qualify for the Good Sam discount. When I register at the park I request the discount, or sometimes a day or two after my stay has begun, and I always have been cheerfully given the discount. I get that it was my fault, but the job of the business is to give excellent customer service. Pissing me off of my request to save a few bucks will not work in their favor, even it it was my fault.