Onboard sound VS Standalone...there is no comparison. People have simply lowered their expectations.
When Creative first introduced their SB16, there used to be other popular cards on the market. One of these was the ProAudio Spectrum 16 and another was the th Gravis UltraSound. The PAS16 actually had better sound processing abilities than its rival, the SB16. It sounded noticeably better in games, where all wave sound was mixed together and output on one channel over the ISA bus. The Gravis UltraSound was one of the first wavetable midi soundcards that replaced the cheesy sounding FM Chip midi with decent quality wavetable sounds. THe result was music that sounded great...Doom's soundtrack was suddenly more like heavy metal rather than a series of bleeps and boops.
One of the reasons I've always kept my Audigy2 around is for midi playback purposes. Say what you will about Creative, but their Emu10K DSP is substantially better than anything you get with current onboard solutions. Soundfonts have always sounded better to me than the DLS which is supported by most other cards.
The thing that people are calling static is the poor signal-to-noise ratio. The Realtek solution is mostly software based, with a chip that is there only to provide support for the physical jacks. It does not actually do any type of signal processing...and the software algorithms it uses are crap. With people shelling out upwards of $300 for a set of multichannel computer speakers, it's not really intelligent to say that consumers don't care about sound. The fact is that they don't know there is something better out there, so they believe what they have is as good as it will get.
For those of you who think that it is feasible to offload high quality audio onto the CPU...it's not. Audio processing is inherently CPU intensive, and even musicians who produce electronic music using software like FruityLoops or CakeWalk do not load up on VST instruments (virtual instruments) for real time performances. Even 2 or 3 tracks with realtime reverb and compression added can suck up the CPU cycles of a Q6600...not to mention the fact that we are moving into an era where games require more CPU power for physics and AI processing.
Finally, the comments comparing soundcards to NICs is also idiotic. Onboard NICs are often crap that do the same thing as onboard sound - offload all the network processing to the CPU. Well, a high quality NIC will handle all network processes with its own DSP. You probably wouldn't need this for a consumer level system, but if you run a server or any type of network situation where the system will be handling hundreds of simultaneous requests at any time, a dedicate NIC will provide 20-30% reduction in CPU usage as well as a more responsive server.