Due to both local and federal laws, stores are required to make certain accommodations. The suit asserts that Apple hasn't done this, taking exception to items being out of reach. They also claim that Apple doesn't have any store policy to help people with disabilities. Ethics aside, there is a letter of the law to follow, and if Apple isn't complying they could easily be facing serious legal issues because of it.
No mention is made as to exactly what the intention of the suit is, but there is a mention that the aim is to get Apple to update their policies and stores over shelling out cash to a few individuals. Earlier this month, Apple was also sued for the paper receipts they print in their stores.