Sound Quality of Direct TV audio

I don't know but would not surprise me if most digital TV providers do something similar. Most people are not audiophiles who care about full range sound reproduction. Filtering out low bass could well make things sound better for many with lesser gear not capable of delivering high quality low bass and either do not care about low bass or do not know what they might be missing.

Low bass is what makes good quality sound production hard. Filtering it out makes things a lot easier and may well sound better than the alternative with a lot of commercial gear out there.

I'd say its almost always a good idea to use digital outputs form most all commercial AV devices whenever possible in that these devices are for mass markets and most audiophiles would prefer results from their own carefully selected DACs, digital amps, etc.