This is their logic. People panic to go buy or update their DVD's / blu-rays when they wouldn't necessarily have gone to buy them. Then in 2 years time they'll bring out the ultimate editions where the biggest potter fans will fork out again for them. Warner brothers have proved time and time again that when it comes to potter they couldn't give one about the fans just how much they can line their pockets with as much money as possible.
This must be the hundredth time I've put this "shame on you Warner Brothers"