I'll echo what Dan, Ted, and Rob said. I'd like to think it's a niche product that's actually doing alright. I suppose it depends on your perspective. I'm sure Sony and all the other large hardware/software companies hoped it would be the next CD or DVD revolution. That obviously didn't happen and won't, for a lot of reasons I won't go into. From that perspective it COULD be viewed as a failure.
But think of SACD and DVD-Audio like you would MFSL. You probably won't see any MFSL releases on Billboards Top 100 either (i.e. MFSL always had a limited customer base). But their products were top notch, as many (not all) of the SACD and DVD-Audio releases are.
I'm sure people can make the argument that MFSL is no longer around (or are they back?), but I don't think most audiophiles will dispute the quality of the recordings. I would guess that the digital hi-rez catalogs are larger than the MFSL catalog for vinyl was/is.
Maybe I'm feeling analagous today. Whatever. But it's similar to Sundance movies too. They aren't usually Hollywood blockbusters like Titanic or Episode 3, and they may not appeal to the millions, but there's quality and care usually put into them.
Lastly, I probably wouldn't spend $1000 or $1500 to try out SACD or DVD-Audio because of the limited titles available, but if I can do it for little more cost than a modest DVD player, why not?