In my view, it's actually worse than that, because many live games get cancelled with a CD, which means they don't end up in the records. So I strongly suspect the proper RRs for some people are considerably worse than it seems.
Anyway, what I want as a user out of such a system is to be able to ensure that my games don't get ruined. From that point of view, as much as taking over a CD is a nice community service, it doesn't actually un-ruin games; it rather helps some games to finish that are already wrecked.
It's also important to understand that Diplomacy is a long-term commitment to a game, and so I'm not really interested in people's last 100 turns as much as their long-term behavior. For example, one of the other forum threads mentions that I recently started 50 gunboat games (thanks again, Valis!) By the end of 1901, I'd have cleared everything on my record except this current series. So, if I'm the sort of person who disappears for a week every month or so, you wouldn't know that from my RR, and yet I'd be very likely to NMR in your new full press game with 3 day deadlines. I'm also the sort of person who feels the need to apologize for my one resign in my profile, a live game that never actually got started, so that probably explains how I feel on the subject.
I can think of one solution which would be easy to program from the current code: at the moment, I can see the details of my RR on my own profile, including which games were involved, but nobody else can. Making that information public would allow a user to argue that they've been better recently, and then people inviting them to games could make up their own minds about whether they agree. Since that information already has code to pull out of the database, it would just be a question of changing one of the flags in the PHP front end.
One other alternative, which is a few lines of code but would also carry good information, would be "Date of late NMR". Again, the idea would be that the RR reflects your entire history, but users have the ability to argue that it should be discounted because of recent good behavior and everybody can make their own decisions, which is kinda how RR is currently being used anyway.