Google Maps actually has the shape of the buildings in my neighborhood incorrect because earlier it was blocked by huge trees, shrouding the shape of the building.
It seems to really struggle with single storey extensions and garages in my area, even when they're nearly as large as the main house floorpan and the Google car drove right past them. I think there's probably human intelligence as well as higher resolution imagery in getting those cathedral and space needle details right...
And it doesn't have any buildings at all in my friends' neighbourhood, because it was fields when their aerial images were taken under construction when their StreetView cars passed through 4 or so years ago. OpenStreetMap has accurate buildings. Apple Maps doesn't, but you've got a complete street layout and can overlay its more recent aerial imagery to see the buildings. Google Maps has no buildings, no aerial imagery from the last seven or more years, gets the street layout wrong and mislabels some of the few streets it actually shows. It's fun taking a 3D drive through the first roads when they were still lined by bare earth and areas about to start construction, but I got lost using their map...
Any mapping service's "moat" depends more on whether it's remotely adequate for the areas an individual cares most about than its ability to superbly render famous features of priority US cities.
In larger cities, such as Chicago, the building shapes are part of the data the local government makes available to the public. All Google has to do is translate it into its format.
