For market share Android overtook iOS and will just make a bigger gap in future in its favor (market share)
As for how markets work, android market is more open that iOS. You register as developer for 25$, make your app, upload to your account and that app is available for download on user devices in 0-30 minutes. You can upload unlimited number of apps. Also you can distribute your app on other android markets, not just Google`s, which you can not do on iOS. Apple iOS market price for developers is 99$/year. And when you make your upp, you upload it so apple can review it. Review process can sometimes last for month or two, and your app can be rejected for various not that obvious reasons and you can do nothing about it.
As for the apps, both iOS and Android markets have basically same kind of apps. iOS currently have more apps, but just tiny percent of all apps are useful, rest are garbage and spam. So both android market and ios have about same number of useful and good apps. And again, all numbers for the future go in favor of android market and it`s growth.
I agree that book is not appropriate for this kind of data. Just google from time to time, that keywords and stats that interest you, because it changes really fast.