At least some (if not all) of that can be explained by rating inflation. The same gap in ability translates to many more points today than 40 years ago.
>The same gap in ability translates to many more points today than 40 years ago
Not really. Ratings inflation means you can't compare the absolute values, but is much less noticeable on ratings differences.
So 2660 + 4.7% = 2785 (125 points) in 1972.
The equivalent today would be something like;
2750 + 4.7% = 2879 (129 points)
The same gap in ability translates to only 4 more points.
Actually even that modest difference should not arise from ratings inflation. That is because the Elo system is based on the idea that a given "gap in ability" is supposed to yield a constant Elo delta. An Elo delta of 100 points is supposed to translate to a 64% score for the stronger player, a delta of 200 points to 76% etc.
Interesting, that sounds reasonable, but two questions:
1. Is it certain that rating inflation is linear?
2. Is there actually any evidence that the constant Elo delta property actually holds even with inflation? It's well known that Elo is flawed, which is why people have been working on alternate rating systems...
I am not a ratings expert, just a (serious) player, chess programmer and amateur chess journalist. I am not sure ratings inflation even exists. If it does exist and you are talking about rating differences between world class players, then you are talking about small differences in big numbers and you are going to get a good approximation to linearity. But it's only approximate because in my previous example the linearity yielded 125 points v 129 points when the key underlying property of the system requires 125 points v 125 points. But unfortunately I don't know the answer to your question 2), I don't know how robust that property of the system is.
Why do I say ratings inflation may not exist ? It is true that in Fischer's time there was one 2700+ player. Now there are 30 or so. That's the evidence for ratings inflation. But it seems likely that the top players are just better than they used to me. Maybe there really are 30 players today who can play at 1972 Bobby Fischer level.
One statistician has developed a system to compare players across time. I don't know enough about statistics to say if it's valid or not, but it's interesting to look at. Unfortunately, it hasn't been updated in almost a decade, since it says Carlsen's peak rating was 2556 in January 2005. http://www.chessmetrics.com/cm/
