> Realistically, frequencies around 20 kHz will create audible artifacts (aliasing)
The energy of the signal components above the Nyquist is generally very low, and very few double blind tests have given any indication that humans can detect the resulting aliasing (even though many people claim to be able to do, almost always in non-double-blind environments).
Badly written digital synthesis can generate high energy signal components above 22kHz, but that's because they're badly written, not because the theory is wrong.
The energy of the signal components above the Nyquist is generally very low, and very few double blind tests have given any indication that humans can detect the resulting aliasing (even though many people claim to be able to do, almost always in non-double-blind environments).
Badly written digital synthesis can generate high energy signal components above 22kHz, but that's because they're badly written, not because the theory is wrong.