gosh I haven't heard of xvid in a long time. It was one of the earliest "open" h.264 implementations, copying the commercial divx codec, and quite impressive at the time (early 2000s) Since that time better implementations have come along, so it's not really relevant anymore. According to Wikipedia, any playback device that supports MPEG4-ASP can play xvid encoded content.
DTS is a licensed technology, so maybe Samsung doesn't want to pay to license it, or doesn't want to implement one of the open source decoders? That does seem odd. DTS and Dolby are both very old, but DTS is far from on its way out. Some of the best sounding movie discs' I've watched recently used DTS-MA, they sound great even though my system is setup for Dolby Atmos