Originally, Kickstarter assumed that all customers would be in the US. Very quickly, they added a function for an International "upcharge". They've now broken it down further, allowing project creators to state different amounts of shipping and handling for a variety of locations.
OK, but why didn't you just keep including domestic S&H in the basic price of a reward level?
It turns out that this was causing overseas customers to be levied too much in import duties, which really wasn't fair. You aren't supposed to pay customs or import taxes on shipping & handling, but if it's included in the price, the taxing authorities certainly calculate it that way! By putting the shipping and handling as a separate piece for everyone, the stated price for customs documents reflects only the value of the reward itself - not a value inflated by the cost of domestic shipping and handling.
We apologize for any confusion this causes, and hope that it does make things run more smoothly for our backers outside the US.