In no time flat I can think of a handful of reasons why Apple has exposed their mapping data through an app rather than a web site. Firstly they probably can't expose it on the web even if they want to due to licensing restrictions on the data they have sourced. I wouldn't mind betting they signed for non-web rights. Secondly by having the data in an app on iOS and OSX they can integrate the two via iCloud such as with shared pins, shared routing info, etc. Finally if the mapping app is local, it can integrate better with other local OSX apps such as iPhoto for displaying geo-tagged photos.
Meanwhile, Apple releases a bunch of fully native web versions of their iWork suite, because it makes sense to do so. Honestly, I expect much better than this from the Guardian.