This is already implemented on the iPhone. The main reason they haven't done it on OS X is that it would be completely backwards-incompatible. They should have

This is already implemented on the iPhone. The main reason they haven't done it on OS X is that it would be completely backwards-incompatible. They should have done it in Snow Leopard (an easy choice if your app uses GC), but if they did they didn't tell anyone. Instead they added optional zip/deflate compression to HFS, and used it for most of the system files.