How'd you go from "will fewer people die of preventable medical causes" to "[i]f Medicare banned hip replacements for anyone older than 75"? To your specific example, immobility is a significant contributing factor for most age related conditions and a hip replacement is an expensive but efficient preventative treatment in old age, especially when it enables the patient to return to regular exercise. Hip replacements aren't like organ transplants where there are a limited number to go around that present an unavoidable moral dilemma. Such a ban would be political suicide for anyone who even proposes it since seniors vote much more reliably so I don't think anyone expects to ship the NHS bureaucracy here wholesale.