This squares pretty well with my personal experience. Pretty much every music geek I know chose an iPhone over an Android because of the music apps
I'm a music geek, I just chose to carry a dedicated music player.
There are some pretty great instrument apps available for the iphone, like the ikaossilator by korg, a tonne of great drum machines, loop apps, synths etc. And mixed with the Audiobus app that lets you route the sound of one app into the input of another (as long as both apps support Audiobus which most seem to do), the possibilities for creating music entirely on your phone are limitless