Thinking out loud, but isn't it hard to say how much standards have improved?
Training is geared towards making strength and stamina gains, but the only way we measure these are with climbing grades - very different from using a stopwatch or a tape measure as in some sports. It's possible that the closer top climbers get to the limit of human ability, the smaller the difference in difficulty between grades, but the bigger it *feels*, so that the progression from y to z requires smaller strength gains than from x to y, but more effort to make the smaller gain.
Then again, grades are as good a way of measuring human ability as anything else. After all, what does 100m in 9.x sec really mean? It's all pretty arbitrary. The real competition, and the real entertainment for the observer, is between the athletes. It's about improving on what anyone has done before, about being bigger, stonger, faster - the grades and numbers are just the agreed parameters of comparison.
But it does make you wonder... Clearly, whatever records are set, no matter how amazing, someone will come along and beat them. The ultimate athlete does not exist. Except maybe Lance Armstrong. So if Moon and Moffatt were in their 20s today, would they still be at the top? Is it a cultural, pyschological thing to be the best, or were they climbers of their time, talented but not as talented as today's top climbers?