The adapter in question allows you to plug a HDMI cable into the DVI connector on the video card. My 4850 card from ASUS had two DVI connectors and no HDMI connector, so I would have to use the adapter to plug it into a TV for example. The card came with one. My later 6850 card has HDMI and DisplayPort and didn't come with one.
Since the 4850 card has two DVI ports, I wonder if the idea was something as simple and stupid as if there are two DVI to HDMI adapters plugged in, only activate HDMI audio on one, and since we assume the user will always use our adapter first, and then someone else's adapter he bought when he added the 2nd display, let's do a simple program check for our adapter instead of a difficult device capability check to decide where to send the audio.
Not a good idea, or even a smart shortcut. More like a last minute bright idea.