So I edited together a video that was originally shot 1920x1080 in Premiere Pro CS6 and put together a video in Encore CS6. In all the timelines, there are slight pillar boxes on the sides of the videos. I looked up Adobe Community help and only saw the community mentioning cropping as a solution.
Okay so I encoded a file from adobe media encoder and brought it into DVD Studio Pro and guess what? PILLARBOXING! It's from the encoder! Okay, I shouldn't get mad at Encore. Will look more into it and get back to you guys.
I believe starting with CS4, Adobe changed the pixel aspect ratios for SD widescreen video upon request from the BBC, which said Adobe had it wrong. Ever since, HD to SD conversions don't come out quite right, leaving those little slivers of black on the sides of the encodes.
As mentioned in the link provided earlier in the thread, there is a cropping solution, you'll have to find it though, sorry I don't have that info handy. I just leave the bars and don't see them when I view my DVDs on the TV.