Uncharted 2: Among Thieves is a prequel.
In all of the promotional material that's been released so far, Nathan is not wearing Sir Francis Drake's ring as a necklace. Since the necklace was returned to him at the end of the first game, and since Sir Francis Drake was revealed to be a hero for dying to protect the secret of the island from getting out, you would think that Nathan would continue wearing the necklace as symbol of pride. If, however, Among Thieves is a prequel, it is very possible that Nathan isn't wearing the ring because he hasn't found it yet, and at some point during the game he will acquire it, realize what the numbers written on the ring mean, and decide to check it out, setting into motion the events of the first game. In this case, it would go without saying that the expedition of Among Thieves is going to be a financial bust, because this would explain why Nathan is bothering to chase after treasures "after" the expedition to the island, why he and Sully were hoping that the treasure of the first game was finally the real deal, and why Sully and Elena are not in Among Thieves (not that we know for sure that they aren't, but Naughty Dog hasn't confirmed that they are, and there is a new female love interest, so at this point I'm assuming they're not in).- Jossed, this game is a sequel to Uncharted: Drake's Fortune.
Shambhala wasn't originally in Asia.
It was in Africa, back when it was known as Gondwana. It floated over to Asia along with the rest of India and got stuck in the mountains.