As we can only guess, I feel support is one of them. The Surface product line truly is aimed at more the "professional" market, and less at the "consumer" market. When you start talking markets all across the world where Cortana, Bing Maps, and other services are not as strong than Microsoft puts itself in a market where this product would not be able to make the impact they want.
I feel you will see the world wide push from MS soon. I know that adding services for world wide support is a major push for them, and a serious amount of capital is being invested in it. But so far, I just do not see the results being strong enough to push these products to all markets.