Curb-cuts may be useful for all sorts of reasons, all of which make it reasonable to require in new construction or replacement, as I said before. None of those reasons mean it (necessarily) makes sense to go through and replace every single corner with a curb-cut, or put a wheelchair ramp in every existing commercial building, or replace every inset water fountain with a water fountain that sticks out into the walkway, potentially posing a hazard…
Requiring these things in new construction to the extent that costs are not substantially increased may not be objectionable with regards to public accomodations, but requiring retro-fits can be very expensive, and often not worth it in terms of providing needed assistance (as opposed to increased convenience). Just how far should government go in requiring expenditures by private (and subordinate public) entities?