Tell me... why would you ever install an app from the sd card? Except... well to steal games. Thats the only thing that I can think of for why you want to... You expect us to help you steal things!?
Perhaps I have used Astro to back up an app (a free app, or all my apps) that I had previously downloaded through the market. Perhaps the developer totally screwed up the app with an update. I choose to uninstall the updated app, and go back to the previous version by installing the apk that Astro backed up to the sd card. Maybe I just prefer to install apps (free, previously downloaded apps) from my sd card explicitly so I won't be bothered by update notifications to those apps.
You have a hell of a lot of nerve to accuse someone of piracy when you don't know the facts.