Maps are core technology on a smartphone these days. We depend on our phones to make calls and otherwise keep us in contact, and we depend on them to tell us where we are and help us find where were are going. We depend on them. Messing with a successful mapping solution on mobile, in any way, is non-trivial.
As Android Central's Phil Nickinson has often remarked -- maps could well be Google's flagship product. (AdSense/AdWords may be their most important, but nothing else comes close to the sheer user-facing coolness of Maps.) As 9to5Mac's Mark Gurman mentioned after Google's own map event yesterday, Google has devoted years to building out and developing their Maps service.
How will Apple replace all that in iOS 6?