Think of it this way, each market is independent, and the price for each market is set based on competitive pricing from other brands within that geographic region. Although there is a fairly signifficant price skewing of the S5, when you compare two regions, within the US region, the price of the S5 is competitive with other manufactuerers from the US, Japan, England and elsewhere.
So, as with any global market, the manufacturer must look at that market to see if they can sell their car at a competitive price.
In this case, you've seen a number of postings which comare the BMW 335, to the S5 and A5. When we examine features, and price, we see that this is a relevant comparison in the US.
Lastly, remember that in the US, the Corvette sells for as little as $50K, but I'll bet when it is shipped overseas, it can sell for more, because it is competing with the European market, and the brands within.