"Okay, you can manipulate it by deleting the favorite and adding it again. But how many people will bother with this and how often?! "

Just to clarify , this wouldn't work. The system will only count it once. If you delete and re add, it doesn't count the add again from the same member. Just an FYI. 

This is one of the things the programmers put into place to cut down on abuse of the ArtCharts as we did not want to go back down the Hot20 path of abuse.