The 16:9 denotion is from the DVD specification notation to let consumers know that its a 16:9 enhanced disc.
16:9 is a moot point with Blu-ray Discs but a lot of studios still state 16:9/16x9 on the artwork. Warner does it on their US releases, the back of Harry Potter and The Half-Blood Prince states: 1080p High-Definition 16x9 2.4:1.
And oddly, my copy of I'm A Cyborg...But That's OK import from Tartan UK states Anamorphic 1.77 on the back.
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