Maybe the problem is that Nitro requires that an app have special permission to mark pages as executable. Apple may be comfortable giving this permission to Safari (or any if their apps, for that matter) but not comfortable giving it to third party apps. Along the same lines, it could be that apps saved to the home screen don't get Nitro because there is a special exemption low in the system for Safari, and they haven't yet worked out how to roll it out to the thin apps that are created when you save something to the home screen.