We would have expected Microsoft to wait a little longer before making such an announcement. While, there's always going to be some support overlap concerns when moving between two platform versions, it's worth noting that the flagship Nokia Lumia 900 went on sale in some markets less than 12 months ago.
From the Skype blog:
Earlier this year we outlined Skype’s Mobile Future, where our work on Windows Phone has been leading the way in a number of key areas. Skype for Windows Phone was the first Skype mobile app to have HD Video Calling, the new Modern user interface and be always on and power efficient. The Windows Phone 8 platform is gaining good momentum in the marketplace and at Skype the vast majority of our Windows Phone base and usage is on Windows Phone 8.
Just recently we released Video Messaging for our Windows Phone 8 app, enabling you to record and share messages, even when friends and loved ones are not available for a call. As we look ahead to the future, we are focusing all our efforts to bring great experiences and improved performance to Windows Phone 8, building on the capabilities of the platform. As a result we are not planning to release further updates to Skype for Windows Phone 7.
The Skype blog goes on to note that it is working on "even more great experiences for Skype for Windows Phone", but does not provide any specifics, perhaps to avoid raising the ire of Windows Phone 7 users, who will now not get any future updates.
A logical path for Skype on Windows Phone in the future would see the service more tightly integrated into the platform, perhaps as a built in app, although that may make it more difficult for the fast moving Skype team to keep the service experience up to date.
More information is available on the Skype Blog.
The Windows Phone Skype app can be downloaded from the Windows Phone Store.