Apparently, WP7 is selling more units at launch than Android did. Does that surprise anyone? Well, it may surprise those who thought it wouldn't sell anything at all, but if it had half a decent chance to grow in this very young market, you shouldn't be too surprised that it's growing faster than Android at launch. Let me explain.
#1 Nine vs One
Microsoft launched not one, not two, but nine phones with the help of its partner manufacturers, and it did it in 30 countries and on 60 carriers. This should by itself mean that WP7 growth should be higher than Androd's initial growth, because there was only one phone on one carrier when Android launched.
#2 A lot of money in promotion
The rumors say that Microsoft invested $500 million to get WP7 started. The money went not only to advertising campaigns in all those countries, but also to pay developers to make apps for them, and I would assume they also paid some to their partners for R&D, so in case WP7 is a flop, the manufacturers' costs will still be covered.
#3 Different times than in 2008
You know how they say that it's the hardest when the market is young because it's basically nonexistent? A lot of companies wait until the market is "more mature" because until then it's pretty unproven.. I would say the iPhone and Android phones paved the way for WP7 phones. It made it easier for them to sell, because they opened people's minds to smartphones. Up until iPhones and Android phones, most people were still using dumbphones, and only geeks and professionals were using smartphones such as BlackBerrys. They unlocked new markets, so it's easier now for other competitors.
So the bottom line is that it's nothing special about WP7 phones selling more than the very first Android phone. The hard part will be for them to keep, because in order to gain market share from iOS or Android, they would need to outsell them. If they only sell 1 million phones per month, while Android sells 10 million, they'll fall farther and farther behind in market share. To gain market share from Android, WP7 would need to sell more than 10 million phones per month. But it doesn't look like Android will be standing still either.