Store offerings are being compared to the highest quality physical release available. Other streaming services are not currently being used for comparison.
In the case of Dirty Dancing, The physical release, along with the BD quality K offering, are available in 7.1. The 4K offering from K is only in 5.1, hence the lower quality designation.
Hope that clears things up.
Thanks! That helps. I personally am not interested in whether the 4K Store version has worse audio than a lower resolution version. But there may be others who might.
However, this is a great starting point on this! Thanks for putting this together!
John