Why do we follow Shannon's Theorem in audio sampling?
What your professor probably meant is that in most audio converters a small amount of aliasing is permitted (for example if you put 24.1khz into a 48khz converter you will see an output component at 23.9kHz that is not very heavily attenuated). The reason for this is that manufacturers like to use so- called half-band filters in the decimation chain because this saves a factor of 2 in the number of multiplications. Halfband filters impose a response symmetry around FS_out/2 so the attenuation at Nyquist is only 6db.  Since this is above the audio band it is not audible. However if you attempt to use this shortcut at lower sample rates like 8khz, it can be quite audible so it is not a recommended technique for lower sample-rates. 

Bob