Sometimes marketing is a big factor. If Samsung promote aggressively and work hand-in-hand in each country major service provider, you can see more of the products on sale and indirectly lead to customer awareness. So although Samsung is quite visible in US, I doubt it is that successful in China and other countries cuz there are so many other brand competing with them there.
As of today, I have tried Motorola,LG,Samsung,HTC and each have their pros and cons. For hardware longevity, Motorola still my choice. I am now testing other brands to see how long they can last.