It's what their client base demands. It's part of their success. Think how many internal tools are relying on compatibility since they would be too expensive

It's what their client base demands. It's part of their success. Think how many internal tools are relying on compatibility since they would be too expensive to rewrite. (I'm looking at you VB6) You may be interested in this technet article on the concept of Shims http://technet.microsoft.com/en-us/library/dd837644(WS.10).aspx http://technet.microsoft.com/en-us/library/dd837644(WS.10).a... Not only can you make your own, Windows ships shims with each release to provide compatibility support with popular user applications. Edit: fixed some grammar.