True, the dvd-a/sacd have limited availability, but I don't think that is the main reason the sales of both are small.
In the world of CE, the big focus on HT is the video. Most people would rather spend big bucks on a large flat panel and then buy a HTiB for the sound, or at the most, a system not much better.
The number of people interested in hi-res audio, in any format, is quite a small percentage, by comparision.