It's always the same story. The UI isn't good enough. And then when iOS users actually use an Android device, they find out that the UI has actually been rather decent since Gingerbread as the OS looks fairly svelte and most major app developers have managed to make their apps not suck. The back button, Activities, Intents are all things that non-Android users are nearly always completely ignorant of and how they affect usability of the device.

Besides the title is a bit of flamebait. Who are we talking about when we say "it doesn't matter"? Investors, developers, users? They all have different considerations and different reasons for preferring various platforms with various outlooks.

edit: Just like with navigation concerns, please actually try some apps. I am the first to admit that Android apps have lagged behind iOS apps in terms of beauty, but there are several that are now so good, I prefer them in terms of appearance. The stigma has stuck around for longer than I've found it to be true. As for stuttering issues, JIT, more ram and Gingerbread have made these largely non existent. (If only they didn't ship Launcher2, the community launchers are a much better experience. Go Launcher EX and stock Gingerbread is absolutely as fast as iOS, even while streaming from SubSonic, etc)