But I think the definition you point to is part of the problem. By saying "Luxury" it makes it sound like staying alive 20 extra years is the same thing as buy

But I think the definition you point to is part of the problem. By saying "Luxury" it makes it sound like staying alive 20 extra years is the same thing as buying a BMW and people tend to reject that. But from a purely analytic standpoint the two situations are similar. A luxury is something of value that most people don't have because it is cost prohibitive. Well most people outside the western world don't live as long as we do and aren't as obese as we are. Because they don't have the money to pay for the health care that we do. So in the limited confines of the study I think their assessment is accurate. With the caveat being their study was very limited in that it doesn't address individual acts that would surely bring health care costs down (as an example negotiating on a national level for drugs is sure to brings costs down though it might have other disadvantages)