I'm guessing that sound hardware already exceeds the fidelity most people can discern unless they spend substantial $$$ on speakers and amps and stuff. But advances in video are instantly obvious to everyone, even with a low-cost display (which doesn't add cost because every computer already has one). Even a toddler will complain about a sucky graphics card, yet be perfectly content with the most awful headphones playing simple 8-bit pong noises if the graphics look awesome.
The way I see it, only people with serious audio hardware are much concerned with the nerdspecs on audio cards, anything which seems to meet/exceed the system reqs for the latest software title is good enough for most.
Fanatic audiophiles already disdain CD audio, it just ain't "audiophile" quality. Most seem to be musicians of some sort, and most claim to strongly prefer analog audio technologies even though the reality is they'll just buy the baddest sound card they can afford and do their day to day audio work with digital formats. Maybe they spend big bucks on fancy audiophile-quality recording software, I dunno.