Why would you need to reason for an execution path? Just use a default one, for everything. All URLs under the path of where the application resides should be passed to the application and the application determines which content should be displayed. Does IIS mandate a file extension of some sort? If so, that's bad.
No, IIS does not. Do you see any file extensions in Channel 9 urls?
This seems to just be a weird (more than likely legacy) case.