Nadal won less than 4 titles in 2011? Damn. Yeah, think he has to since his last non-clay title is from 2010. And Djoko whooped his ass in Rome and Madrid.
The main reason Nadal ended the year as no. 2, was apart from the fact that the other guy won the other 3 slams, but also that Nadal made like 7 big finals, aside from the slam and MS title he won.