David Braue of ZDNet has an interesting idea of why Maps exists in Mavericks:
This lies at the crux of Apple’s decision to move Maps into Mavericks: the company has effectively staked its claim in the idea of what I might call Mapping as a Service (MaaS).
This is the concept of providing a consistent technology platform between desktops and mobile devices that will allow applications to just assume that a certain degree of mapping capability is available with a single tap. Rather than being an optional addon, geospatial capabilities become an intrinsic part of the user experience.
There are all sorts of new and improved location-based APIs in Mavericks; the Maps application has a natural place on the OS as a result. As a result of it being a native application, it feels a lot more engaging and powerful than a web-based tool. Swiping, zooming, and trackpad gestures all provide for a better user experience.
But if Braue is right, my initial doubt over a native Maps application was clearly ill-founded; not just for the reasons above, mind you, but for larger, more powerful reasons.