Good points. Another aspect to consider is that some Android users don't even know that they are Android users. I don't know how many, but speaking from person

Good points. Another aspect to consider is that some Android users don't even know that they are Android users. I don't know how many, but speaking from personal experience, it seems a non-negligible percentage of "normal" Android users simply bought a touch screen smartphone in the lower end of the market, because that's what carriers are pushing now. It's running Android, but the owner doesn't know it, and isn't familiar with any marketplace to download apps. iPhone users though, they know that they have an iPhone and what that entails. Meaning, they know what the AppStore is, and Apple has their credit card information. Some even had an Apple account before they got an iPhone — if they had an iPod previously they can just start buying apps right away. Counting users is one thing, but what you should be counting are active users of respective marketplaces/app stores.