Is there a good measure of success for a platform rather than numbers? Here are a few I could think of

• Services used by users (and potentially paying for them).
• Money earning potential for all who are involved in delivering the services not just from the hardware..
• Opportunities for developers to build amazing apps which directly compete with the manufacturers offering. (look atEmoze, Seven...)
• Promotes openness & innovation in its systems and provides options to customers to change and use the handset in any way they please. (Nokia & Google adhere to this).

The key to deciding which platform to build on needs to consider the above and the commercial reality of getting things done.AppStore has done a real Gold Rush and now many are re-thinking as to how this may materialize. I am not trying to get into AppStore bashing, then again it has changed the industry in more than many ways.