Who would have predicted this in 2005 or 2006? Nadal is 27 right now and Djokovic is 26, this corresponds with Federer's age in 2008/2009. I don't think many people would deny that they are playing better tennis than Roger was at the same age.
I think it has to do with their greater emphasis on being physically fit. They are both clearly in much better shape than Federer ever was. Thoughts? IMO its a shame that Federer didn't train harder, especially as he approached his late 20's. He could have been in much better athletic shape than he was, in terms of speed and strength.
Djoko is born in May, Rafa in June and Fed in August.
Djoko's 2013 corresponds to Fed's 2007. I would take Fed's any day.
Nadal's 2013 corresponds with Fed's 2008, clearly Nadal (and yes, Fed made three finals and a semi, but he didn't win that much beside the two slams).
I tend to see it this way. Fed's winning percentage against the field as well as top-10 dropped dramatically in 2008. From 80-100 from 2004-2007 to 41 % in 2008. He still had enough fear factor and enough game to make it all the way to the slam finals and win some. But not enough to dominate.
Imo - and I know this will be very controversial to some - had Federer not had mono in 2008, it's very likely that the passing of the torch would have waited another year or more. Likewise, had Rafa not got injured/family trouble or what not in 2009, it's quite likely Fed would never have gained that RG title and perhaps even not the Wimbledon-title either.
Imo, they would have been very equal ranking and slamwise in 2008 and 2009, with Rafa (with no injuries/familytrouble), getting the definitive edge either in late 2009 or 2010.
And yes, I know this is pure speculation, but whichever way you want to put it, there's a dramatic drop in Fed's performance in 2008, when he's still only 26 for most of the year. And it cannot in any way be ascribed to Rafa alone (Rafa beat him 4 times in 2006 as well as in 2008 ).