WP7 can finish a very distant 3rd place in North America and still be #2 globally. Nokia can lose the European crowd and still dominate in volume sales. It is no different than Xbox 360 being a hit in the U.S. and being a flop in Japan.
Outside NA, Nokia's brand recognition is BIG. China and India make up 36% of the world population and each over a billion. Indonesia ranks 4th. Pakistan ranks 6th. That is four Asian countries in the Top 6. Then you have Bangladesh, Japan, Philippines, Vietnam, and Thailand in the Top 20. Nokia targets Asia, and they will continue to sell in large volumes. They can lose Europe if the Euros hate an American company like Microsoft and still be #1 in sales. All the European countries still won't make up the entire population from China and India alone. Nokia would never lose Europe though. It is the only European powerhouse in the cell phone industry that exist there and they will still pride Nokia over there. Most of the major players are American or Asian.
True, many Asian countries' income is much lower than NA and Europe. Doesn't matter. Not everybody can afford paying for iPhones in those poorer countries either. And iPhones are more expensive over there in those "poorer" but developing countries. Ten years ago, many Americans didn't even know what texting yet. It didn't catch fire until a few years later. I remember visiting Manila in November 2001 and texting was already big there. By 2002-2003, Asia had 3G and cameraphones. It is the reason why Nokia never wanted to target their smartphones for the American audience. They don't care. Nokia's smartphones were big and ugly compared to our thin flip phones, but they were more versatile and powerful.
It is a global perspective and not just certain continents. That is why people who scoffed at the Microsoft + Nokia deal don't have the foresight to know how big it will be in the longer-term and globally. To criticize a 4-month old OS when many people are stuck with a contract and only looking at sales domestically is being myopic about it. Reach out to Asia and you win volume sales.
iOS vs Android vs WP7 is the three-horse race in the mobile OS wars.
BB OS 7, webOS, and Meego will be for the core/niche crowd. I think of it like Linux or people who are smart enough to use Firefox, Chrome, or Opera over Internet Explorer. They could be superior browsers, but will be less popular. Symbian will be demoted to the lower-end.