Just look at what Federer did in 2005, following up his first "big" season. He successfully defended:
Dubai, IW, Miami, Hamburg, Halle, Wimbledon, US Open
So far Djokovic has only defended the AO. He is still defending 7 more titles(Miami, Serbia, Madrid, Rome, Wimbledon, Canada, US Open). If he can defend all of these titles then he can say he did better then Federer's 2005 season.