I know nothing about that he'd stated anything about Nibali's chances on GTs, maybe so, (could be based on results in that time), but I think rather by others than by himself. Yes, last year was definitely more disspointing, but change of team could play role, look a Lulu for instance and many more. 5th place in Giro was best 2011 result so far, then injury on TdF. After that first race was Strade bianche where he worked for Iglinsky yet managed to finish 6th, than 3rd place in T - A, 6th Trentino with decent performance on Punta Veleno, definitely best in category of normal human

I donť know if Nibali exceeds expectations cause I don't remember somebody stating that he couldn't perform one time in future as he performs. Kreuziger had very good results very young, than he stagnated a bit, not getting worse IMO. Only those putting too big expactations were disappointed.
maybe situation in Liquigas by that time was such that he wanted to change team cause they begun to prefer Nibali as Italian, same as we could saw with Sagan recently. Maybe he hadn't conditions good enough thus stagnating...