I'm thinking it goes something like this: Let's assume Apple's map quality is more or less resolved within the near future and put it aside. What can they do with total control over a POI+venue database?

-- They can generate statistics on who's searching for what, when, and where from and sell that off or give it away free to venue operators.

-- They can link custom Apps and content to a venue. (Welcome to the Museum! Tap here to download a free tour guide.") They can link .passbook offers directly on-map. ("Tap here for a discount on entry, today only!")

-- They can sell off preferential search results, preferential ratings, or retargeted advertising like Google and Yelp do.

-- They can do the opposite of that and proclaim that their maps and venue listings are of unimpeachable quality without gamed results

-- They can create a meta-venue datatype through Apple Connect that allows authorized entities to quickly whip up appealing micro-sites for their venues "Drop your menu .PDF here"

-- They can do anything they want with in-venue navigation, which is going to be massive now that the interior mapping tools are coming onto the market

With all this done:

-- They can API-ize this and create mini-sites or mini-apps wrapped in Yelp-y context that replace the entire idea of how you interact with a venue. For instance: "Thai Bistro" is now an App that tells you exactly what's going on with your favorite joint without consulting twitter, facebook, a webpage, and a mapping service.

In short, with this map platform they can now own the total experience of -leaving the house-. Google is years ahead of them on this, and it's unlikely Google's willing to share their advances with their frenemy.

Maps are foundational to representing the state of the civilization around you. It's the Webkit for Real World Experiences.