In 2008 the generation after were meant to start being threats on all surfaces. But what about all the years before then. When Federer joined the tour, there were no immediate ATG from the generation before his, we still need to skip a generation to get back to Sampras and Agassi.
In two generations, we basically had ONE ATG and that was Federer. Between 1972 and 1985, only ATG born was Federer, heck, even if he didn't have any immediately ahead of him, he should have at least had one in his own generation, but Safin, Hewitt, Roddick, Nalbandian couldn't reach that level....it took until 1986 for another ATG to be born.
This is quite the period for inflation for any ATG to take advantage of. What happened in 2008 was the natural order, Nadal was 22 that year, he should be a threat everywhere.
This is why so many have called that period an inflated period for Federer, he didn't have anyone that was ATG for years. When the guy is facing 35.5 Agassi in the USO final during his peak years, it shows how bad it was. Oh well.