Security seals on top and the difference in weight/feel

[Xyberfaust]

I went to Best Buy yesterday and I was checking out the Warner Bros. Blurays. They have the $5 coupon Dark Knight Rises promotion going on where they reissued a bunch of great titles and slapped these stickers/coupons on the outer plastic packaging.

I noticed that they were mostly lacking a white security seal at the top with the title of the product. The cases also felt hollow when I compared them to the very few that had a white security seal at the top. The ones with the seal felt tougher, less hollow and like there might be more content (extra disc?), like they were airtight and sturdy while the ones without you could pinch them and they deflate in a sense.

What's that about?