It's a bit like the Barcelona situation..but not really their fault that they are so bloody great at football/tennis..and in tennis it's quite incredible that you get 3 great, great players at the same time (and Murray, who's not far off)...
It's a bit like watching the Barcelona-Real Madrid game when both are playing well, the level is so high, everything is decided on the smallest of margins..
For me it has a bit to do with the demise of American tennis in the post Sampras/Aggasi era. Its eerily reminiscent of the mid 80s when Lendl had a run at the top, in fact Djokovic's generic demeanor reminds me a lot of Lendl - just as the energy of Rafa and Fed are mildly reminiscent of McEnroe and Wilander. The sport definitely needs some new top players to break through to reinvigorate some spice at the top.