the practice is way too common than you think especially in bigger corp.
Posting is just for the show really, so the person who didn't get hired can't say there isn't any posting for the specific position and go HR to file a complaint.
Also every posting at the end will say similar to " only suitable candidate will be contacted ", so they will never need to speak to you or setup useless interviews.
I been to that situation before, the good end that is...
