Un bel giorno Abstract Dissonance digitò:
It's the standard because when you are going to do the mixing/mastering, there could be more (sometimes much more) than one source, therefore you need more dynamics. I suppose that they use 24 bit even for the single sources just for a matter of homogeneity, not certainly because they are needed to record a single source properly. Probably even the 44 kHz, 16 bit CD quality is overkill.
Very good, then why don't you just use a 16 bit ADC and add eigth or sixteen padding zeroes at the end? No one will notice, unless he has an oscilloscope. :-)