Google Play Vs. Apple App Store
App Store: Apple puts a lot more of emphasis on selling music and movies. This is probably because they are trying to promote iTunes, the biggest digital distributer of music. As soon as open the App store, it shows different categories, and music and movies are at the front.
Google Play: Google puts more emphasis on games. As soon as you open up Google Play, it shows big colorful icons of the most popular games. They also try to promote music and movie downloads, but it's not in your face like the games.
The app availability at this point is pretty much the same at this point. I remember a couple of years ago, however, that was not the case. This was back when Temple Run was the app everyone was talking about, and at the time I only had an Android and not an iPod, and Temple Run was not available on Android yet. I believe the same was true about Subway Surfers. The flipside though, was my favorite app, Defender 2, was only available on Android for a while.
In terms of number of apps, Google Play has passed the App Store. Despite Apple's large lead, Google Play was able to catch up and be the first of them to hit 1 million total apps.