@acid_kewpie: I have just tried out what you said:
- The owner of a file can NOT always delete it, only if he has write permission for the directory containing the file
- Using chmod -w on a file does NOT prevent other users from deleting it, it only keeps them from changing its content.
Linux apparently does not regard the deletion of a file as a writing access!
It seems to me that a file can only be prevented from being deleted by disabling the write permission for the directory containing the file - and if this is true, there is a major design error in Linux access rights.