A USB audio interface also lies outside the electrically noisy interior of a PC chassis.
Strong caution with USB audio. There is a metric buttload of cheap USB adapters, While they technically work, they typically lack analog filtering that gets rid of higher harmonics. If you look at the output on an oscilloscope, instead of a smooth wave, you see the actual steps. Better audio hardware should have filters to smooth this stuff out.
Another MAJOR thing is inducing noise into the output. This is not just for USB cards, but all audio solutions. You need some pretty good filtering between the digital and analog power domains -- yet another area where cheap sound can skimp. Hey, let's shave $0.05 off by dropping this capacitor and inductor!
The original article really touches on two separate areas:
1) Audio processing
2) Higher quality audio circuitry
SoundBlaster (and other gaming-oriented cards) typically do both. However, do you really NEED both? The audio processing stuff is supposed to provide an API that games can use to make thing sound more realistic, or offload audio processing from software to hardware, or both. It can typically decode various dolby flavors, and do some other fancy DSP-ish type stuff. Do you really NEED all of that? If so, then maybe a gaming card is for you.
However, what if you want the best sound possible, the lowest noise possible, and don't really game or use the various audio enhancements? You just want a plain-vanilla sound card, but with the highest quality audio. Where to do? Skip the computer store, but go to your local MUSIC store (not the ones that sell CD's, the ones that sell GUITARS). Those cards skip all of the DSP bells and whistles, but have the best-quality DACs and filtering that you can find. You can find some really good USB solutions that will blow on-board audio out of the water for about $100 or so. Of course, you can go crazy and spend $500 or more if you want. If it is good enough for a music producer to use in a studio (who makes his or her living off of the sound), it is probably good enough for YOUR music and movies.