Better medical technology = an accident that is fatal now may not be fatal a hundred years into the future. All these studies are complete bullshit because none of them can predict the social factor and over a period as long as 2500 years, it dominates everything else.
This social factor includes murders and other petty crimes, as well as holocausts, wars, and things of that sort, all of which have a tendency to reduce lifespan, and none of which would stop just because we live 2500 years.
Maybe maybe not but who here is willing to make any bet on what technology we will have in 2500 years? I certainly am not. And thats just one example of something that could (and is likely to) change drastically.