New operating systems often bring new functionality to the table, and Microsoft's latest iteration of Windows Phone is no exception. One issue that developers face with new software is deciding on the future of something they have poured hours into creating - but Microsoft might have a solutiion.
The WP Market allows multiple XAP files (information on the .xap file's specifics here) under the same GUID. Numerous versions of an app can exist under the one developer, with details being tailored to fit a specific OS.
The Market can identify the version of Windows Phone in use, letting WP7 handsets see only WP7-compatible apps. WP8 handsets, boasting compatibility for older apps, can see applications for both. Should a developer want to make the app WP8-native, they can also automatically automatically update their app using Microsoft's Visual Studio software.
The efforts all seem to be focused on maintaining WP7's position, at least for a little while longer. Bigger developers might wish to concentrate their resources on WP8 but at least this way older phones can still use, and find, applications.