I agree that it would be great, but I think the limitation is lack of resources in the ICS department (that is, all resources are focusing on other priorities). Windows 8 does have a Gospel Library app:
https://tech.lds.org/wiki/Gospel_Library_for_Windows_8
Windows 7 does not, nor does OS X. I don't think the church has developed any apps that run on OS X, apart from the Java-based Indexing software – so I wouldn't be surprised if there are 0 developers at the church who develop for OS X.
I believe that the Windows 8 app was started by a volunteer and donated to the church. The same is true for the LDS Music mobile app. This is the most likely way for a Windows 7 or OS X app to get officially adopted/developed by the church.