Yeah this is nice, but the problem is that Android and iOS aren't going anywhere anytime soon. WP is going to have a hard time winning over a good portion of those people. On the other hand, there are still many people who don't have a smartphone. MS should focus on those people.
As far as investing in an ecosystem, I can understand that. I invested some money (not a lot) in Android apps. I didn't want to lose all of those. The great thing is that I have had an Asus Transformer for about 6 months and I can still use all my apps on that. So now I don't feel like those apps are going to waste. Some people may do the same with iOS. Get a WP and keep using their paid apps on their iPad. Who knows.