I don't think he means frequency alone, but different methods of buffering and mixing, perhaps with random pitch support and 3d spatialization/doppler as well as echo/chorus/reverb. 44khz sound is not going to magically make Quake catch up to Half-Life.
the only higher rate sounds in Quake are fish chomps, an unused shub 'omnomnom' (eat that hwguy) and a lightning gun zapping.