What are you talking about? I own several programs I bought before Mac App Store launched and store shows them as installed. I am pretty sure, that if you delete an app and then try to "buy" it again, you will get the same as in iOS App Store: a prompt that you already own this app and suggestion to redownload it.
I just deleted CoverSutra which I purchased this morning off the App Store and it went from "Installed" to "Reinstall" or "Not Installed" (I can't really remember which) and I was able to reinstall it with one click and it came flying back into my dock. Pretty darn easy if you ask me. However, I'm not sure if the purchases are stored locally in the app itself/cloud? Say, If I just got a brand new machine, would my app list be stored in the cloud and ready for my viewing if I logged in with my account in the App Store? I'm not quite sure about that part though.
The site suggests that you'd be covered: "You can install apps on every Mac you use and even download them again. This is especially convenient when you buy a new Mac and want to load it with apps you already own."
