> Who has to look up anything? We're talking about a URL--the software does the lookup and the user just sees the correct map.
On the contrary, we're talking about friendly URLs, comprehensible to normals. A human can compose a URL of the format proposed by the example, and have it point to the correct map. With lat:lon URLs, the human would have to geocode their address into lat:lon then compose the URL.
However, to agree with one part of your point, software manages to accomplish that today: put in an exact mailing address, and get a pin on a map. Therefore, one can obviously parse an address from a URL, and get the same pin on a map. Best of both worlds: human friendly URLs, while supporting lat:lon for any non-address POI.