On a tablet, the most important content sources are videos, e-books, and periodicals — all areas where Amazon excels tremendously. On a smartphone, the primary content source is apps. Of course, people use a lot of apps on tablets also, but apps are much more critical for smartphones than for tablets. Amazon has a strong selection in its MP3 music store, but those are DRM-free and playable on all devices, so there’s no advantage there. When it comes to Amazon’s Appstore for Android, it lags by a large margin.