Yes - exactly the same issue here. Seems to affect both iOS and OSX MKMapView equally. Also when you attempt to zoom in beyond a certain level the tiles simply disappear i.e. the system does not even block the user from zooming in further than it can support.
Very disappointing, given that the Apple Maps apps do show much higher resolution as well as successfully preventing zoom beyond the availability of tiles.
Many applications of maps, including my own, rely on hi-res imaging. In my iOS app I therefore use Google Maps instead. However, on OSX it is technically difficult and expensive to use Google Maps, so I'm kind of stuck - its basically preventing me from releasing an OSX version of my app.