Its not just about being able to test (although I have serious doubts that any suite of emulators will be able to give anything more than a rough guess as to how an app will perform on a wide variety of potential platforms) but also about what features will be available, what APIs will work, and how much code you will have to write to deal with some funky condition on Vendor A's phone that makes it differ in some subtle way from Vendor B and C's phones. Eventually they will probably figure it out, but for the next year or so this game is going to make browser feature detection look like a walk in the park...