There are pages that are not 3030, but that's because they're not games. You don't have to worry about those.
Incrementing the offset should get you all game pages, unless a page is deleted while you're doing this causing another game to shift to a previous page and not appear in your results. That would suck.
I was snooping around inside Steam for Android's APK one time and was shocked to learn that it actually uses Fragments. It looks and feels like the entire app is a WebView, but apparently it uses Fragments to some extent.
Of course using Fragment doesn't make an app automatically great, but it typically indicates an understanding of the platform, which I'm not seeing in the app.