Scott Andrew thinks he knows why Google Maps wins:
It occurs to me that the real winning feature of Google Maps is not its DHTML-goodness, its endless scrolling surfaces, its Ajax underpinnings nor its satellite photo views. Rather, the winning feature is the user types the address into a single input box. No more entering street address, city, state and zip into separate boxes. You don’t even need commas, AFAICT.
Good point. I always liked how in England I would just get asked for my house number (18, 213 #B, etc) and postal (zip) code. With that information you can calculate every location in England.
If we could really push the whole zip+4 then we can get the same affect. Right now if I put in my zip+4 to Google Maps, it just gives me the high level of the 5 digit version.