I'm not trying to say you're wrong, but I get the impression that the reason Apple doesn't have something like that is that they think it will ultimately be worse for the user experience. Frequently they seem to eschew flexibility and customizability in order to simplify the interface. You could say they go too far (though I'd personally disagree in most cases), but I don't think that they simply overlooked features such as that.

This map, though, looks like it could be part of the iPhone default apps.

Ultimately, if they had a real keyboard and a better network, it would be better for this users' experience.

I agree on the keeping it simple part though. No need to make everything customizable when you have people that can make things more beautiful than you can. Sure, you can customize your version of van Gogh's Irises, but why bother? :-)

Customizing isn't just about beauty. It's about getting and organizing and using your phone's features in a way that make sense to you personally.

Would you buy a computer that couldn't be customized?

For some kinds of customizability, certainly, yes. Why not?

Yes. I own an XBox 360.

They get a nice cut when someone buys a $50+ navigation app on the iPhone. I don't see Apple making this or any other navigation app a native application and ruining the market that already exists.

They could also get a lot of third-party revenue by wiping out all of the native apps and letting other people sell them. At some point you have to worry about the value of your platform and now they have Android to compete with.

I think Apple's recent acquisition of Placebase, a mapping company, might indicate that they're willing to compete with Google on a navigation app.