Reasonableness is generally a part of determining accommodations for disabilities. For many games, there are no reasonable steps to make them accessible to someone with a sensory or mobility impairment. But there are also reasonable steps that can be taken, like captions for recorded dialog for the hearing impaired or color/pattern alternatives for people with color vision deficiencies (I don't think color vision deficiency meets the legal definition of a disability but it's still something to keep in mind).

A site that offers games to download can be very accessible but the games themselves might not be and don't have to be; not every product a store sells has to be usable by every potential customer. That's not a reason to not make the site accessible; e.g. a disabled parent should be able to download a game for their non-disabled child.