Dolby Digital is REQUIRED by the DVD-V format, while DTS is strictly optional. I think Universal uses it more often than other studios. Also, DTS is used only when the original audio material is in at least 5 channels; you'll never see DTS used on a DVD with, for instance, only a 3-channel Dolby Surround track.
I expect Netflix issues the same original discs that we can buy or rent; they just don't pay attention to whether a disc includes a DTS track. Simply cycle thru the Audio options when the movie starts to see if DTS is there.
I agree with Flemingjrd--DTS sounds better.
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