I don't really see that this is a trick necessarily.  From a general SQL backup point of view (not just diff backups) you should be aware that SQL can store multiple backups in a single file.

I think it would be beneficial for people to be made aware of what a differential backup is, how it is different from an incremental backup (ie transaction log), etc..

In any case, thanks for sharing an article - I'm sure many people have been caught out by not using the INIT option when doing their backups.