My apologies: I’m afraid we will not be able to offer upgrade pricing to our Mac App Store customers after all. So long as we continue to sell our apps through the Mac App Store, we are not allowed to distribute updates through other channels to apps which were purchased from the App Store.
The program Case is referring to was called OmniKeyMaster. Here’s what it did:
OmniKeyMaster is a simple app that finds App Store copies of Omni apps installed on your Mac, then generates equivalent licenses from our store - for free. This gives Mac App Store customers access to discounted pricing when upgrading from the Standard edition to Professional, or when upgrading from one major version to the next. Another benefit: since they don’t have to wait in an approval queue, our direct releases sometimes get earlier access to new features and bug fixes. OmniKeyMaster lets App Store customers access those builds, as well.