Whether it's the kind of discrimination the store is obliged to deal with is going to come down to principles of reasonable accomodation.
So, say you had an extremely boutique store up some rickety stairs, where the way it's used is you go up the stairs and meet the chef who will take your order for a wedding cake and you can collect the cake next week.
I would expect, in that case, if the chef is willing to meet you at your home or another place with a menu of options and discuss your order, and then have it delivered next week, that would meet the bar of reasonable accomodation for someone who couldn't use the rickety stairs.
On the other hand, a large grocery store, where browsing the goods is part of the experience and is also significant to product discovery, and maybe pricing and access to better fresh ingredients and different bargains, and where the only obstacle is that the store does not replace one door type with another that a wheelchair user can enter, and the store can reasonably afford the cost, that is clearly inadequate of the store; they have no good excuse and could reasonably accomodate by changing that door.
On another hand, the same large grocery store may find it difficult to accomodate people who cannot tolerate bright illumination (that other people need, to see clearly), and large numbers of people moving around them. In that case, it is not at all obvious that the store can do much to accomodate. I would expect that if the store also provides online ordering with delivery, that it has performed reasonable accomodation for that situation.
I bet most businesses would make their stores accessible (within reason) since you need room in isles for carts, etc.
It wouldn't be the only obstacle. Let's take wheelchair-accessible parking spots for example. We have to convince the store that sacrificing regular-sized parking spots (and the ones closest to the store, at that) in order to make room for a smaller number of larger parking spots that are reserved for 2% of their customers (and not exactly the most profitable 2%, either) is a reasonable accommodation.
Bear in mind that some of those spots we're asking them to convert might already be reserved for the store manager, some senior employees, and the employee-of-the-month as perks, rather than for customers. You will have a lot of convincing to do, and should expect significant pushback from the local chamber of commerce.