The opportunity to offer targeted advertising based on a user's location should help these and other firms win a slice (or in Google's case, expand its slice) of the huge market for local advertising.
In short, there's no way I'd consider using the iPhone if the only Google-made app in the iOS universe was a search program. (Yes, that's the casein Windows Phone -- just a single Google app.) The iPhone would still have sold millions, sure, but one has to wonder how much less impactful it would've been without Google pushing its apps into the App Store.