The current grades are more a snapshot of history than the physical limits of humanity, IMO. Like the 4 minute mile, once one person did it, you saw several people after that able to do it. In the golden years of Yose, 5.12 was this crazy thing that only the elite did. Now it's something normal people can achieve. Part of that is technology -- I wouldn't want to ever lead 5.12 without a set of cams -- but part of it is that it's just easier to get to somewhere if you already know it's physically possible.