It is unbelievable that such price was only in South Korea. I suppose the price should be the same over the world, and yes, it can be some little difference on exchangers, because of they set the price themselfs.
The differences in prices like always comes from a supply and demand, while technically you can buy and sell bitcoin anywhere in the world, if there is not much bitcoin to go around then it makes sense the price gets higher, in localbitcoins the price are even higher since all of those people trying to sell there are traders and want to obtain a premium over the current price and if many people want to buy at once that only makes the price even higher than it is.