Well they have, but may not have that good of ears.
Yes M-Audio's cheaper cards will beat out top end soundblasters, but m-audio's cheap card (audiophile 2496) also lack the features of soundblasters (like surround). But for music, you dont need (or want) surround.
However alot of people cannot tell the difference between a crapblaster and anything else. Crapblaster has no large quality control issues or anything, and noone ever has any real issues.
If 2 cards sound the same and have close to the same thing's, it's the bling bling of the crapblaster as well as extra software and marketing.