Hayabusa said:
Nibali will never win the tour. He'll never be able to beat Contador or an on-form Schleck, simple as that.
No one predicted/thought/believed he would win the Vuelta too.
Contador and Andy Schleck are the best GC riders by far and below them is a big pool of contenders with little to no difference in their levels. Crashes/illnesses/bans happen which can give anyone of that pool the chance to win a GT. Nibali isn't on paper even in the top 3 of the best of the rest. But he has his strengths and uses them well and a great team, which can't be said for some of his fellow contenders. You can take Gesink who is better in high altitude, multi mountain stages and has better recovery than Nibbles and has underperformed due to Rabo gross mismanagement, average bike handling skills and bad luck. Or Menchov who suffers from bad positioning and switching off at times. Nibali was brought up the right way, being at first domestique for di Luca, then for Basso in 2010 where he got podium in a very hard Giro which was the platform to be the sole leader at the Vuelta.
Of course not everyone likes Nibali, that's understandable, but even his detractors like Dekker-Tifosi respect that he tries to animate and is competitive in almost every race he enters.