I remember reading a french article claiming proof that we *perceive* sounds beyond our aural limits (through the bones, I believe). If this is the case, wide-bandwidth reproduction is useful: many instruments' harmonics go well beyond the standard 20kHz -- one example being sax (60-70kHz?) -- so why not have them? Likewise, BTW, many instruments' harmonics fall well below their fundamental -- as anyone who has played around listening to the sub alone would know!
Now as to whether such multi-kHz info exists on the s/ware, in the first place, is another matter!
Now as to whether such multi-kHz info exists on the s/ware, in the first place, is another matter!