While a DVD-Video player can play a DVD-Audio disc, it is via backwards compatibility mode. It is accessing the Dolby Digital and/or DTS surround tracks.
DVD-Audio players can access the Hi-Resolution tracks, which can utilizie Meridian Lossless Packing. In addition, this opens the door to 6-channels at 24bits/96K and 2-channels at 24bits/192K. So what you're getting, is a copy of the master tape, as opposed to a good approximation.