Good Morning

I tried searching for my answer a couple of times with out any real luck, so I thought I would post my first question.

I'm a little confused as to why my HDX rentals are not full screen but rather are letter-boxed...

Take for example "Clash of the Titans" vs "Avatar" , both HDX movies are 1080P however Clash of the Titans is letter-boxed as where Avatar is full screen...

In fact a vast majority of movies when viewed on Vudu are letter-boxed rather than full screen 1080P however, this is not the case when I rent a movie thats 1080P from DirectTV ...

Here are some of my stats

TV :
LG 55LE5400 55-Inch 1080p 120 Hz LED HDTV

Streaming :
Download Speed: 25683 kbps (25.7 Mbps)
Upload Speed: 3286 kbps (3.3 Mbps)

Thanks for any insight