I bought my Mellel without any code at the Appstore. What gives?
You do not need to a code with a purchase via the Mac App store.
When you purchase Mellel at the Mac App Store you're using your Apple ID, and that ID is used to register your copy for you by Apple. Which is a good thing: when you need to retrieve a fresh copy of Mellel, you can use your Apple ID to download it, and it'll be registered for you.