While Apple is not offering pre-orders of the iPhone 5s in the United States or other western countries, that's not the case in China and Hong Kong, where the device has practically sold out already.
As noted by MacRumors, Apple likely decided to offer pre-orders of the iPhone 5s in China to thwart scalpers, who frequently line up to buy huge numbers of iPhones which they then sell for a profit. The site also notes that while there is still an available supply of most iPhone 5c's, all but the 16 GB "Space Grey" iPhone 5s has sold out
