I was a littLe annoyed by that, too, but mostly because there isn't an option to pay for an ad-free experience.
Yet I didn't buy the phone for the maps app. I have other choices for maps providers. It is perfectly acceptable to me that Apple charge me for additional services like maps.
What makes it superior in my eyes is the quality of the default app, the note app for instance of the reminder, both extremely powerful and 'free'.
Now if they are going to downgrade their app quality by putting ads in them, it loose it's edge over cheaper Android phone.