Just to add a little to the original question I posed, Mats Wilander has added another angle. www.dailymail.co.uk/sport/tennis/article-4873290/Wilander-feels-Nadal-Federer-continue-dominate.html

His argument appears to be that the younger, NextGen, guys dont have the experience or the savvy to know how to play Rog, Nadal, Djoko and Murray etc over 5 sets and two weeks in a slam environment and this means that the older guys will continue to dominate until they work it out.

That is an interesting point - many years back all events where played over 5 sets but as the tour became more brutal and intense that dropped down. Back in the 80's and early 90's events like Miami would still play the last 8 onwards over 5 sets, then many tour finals where still played over 5 sets, most of the big events maintained 5 set finals for a long while but these have died down as well and it truly is only the Slams and the Davis Cup that still plays over them. It isnt about fitness it is about strategy and emotions over that longer distance, as Wilander says.

Interesting angle and it will be interesting to see how it plays through.