That may not necessarily be true
I mean, many users may have the Professional version (e.g. because they don't fulfil the "home & non-commercial" condition - they use it at work), but they feel satisfied with Simple UI and don't need to create their own tasks, etc. So, the settings they get from the tray icon context menu is exactly the same as the one in the Simple UI itself.
You are right that it doesn't have much sense for those users who know avast! very well, and possibly switch between Simple and Enhanced UI often back and forth... but I believe they are many users who use only one of the interfaces.