If he don't it is because he as chose not too target it as a main goal. Like i said in the predicitons i don't think he can win the TDF next year if he does the Giro. If he did just the TDF as main goal for 2-3 years he as a very good chance but he is now interested in the Giro again as he probably wants multiple GT's in the Giro he also feels robbed i bet after 2011. Their is one man who can beat him in good shape and that is Froome when both in form imo they are close.
You think Nibali is the man nowadays, Nibali is a ducker that is all. "I will go for the double" he said then it is "oh but the team like Aru", im sure a TDF winner picks what he does Nibali has final say on that salary. Nibali know's Contador has is number, you should watch the Giro 2011 Contador toyed with him like a little baby. Nibali had to ride tempo as Contador blew them all up. Nibali was doing the Giro untill Contador announced he would ride no way he thought the TDF would work out this lucky again.