One thing to note: the line where the audio frequency is cut off isn't the sampling rate, it's half the sampling rate (or, to be completely accurate, less than half the sampling rate). In other words: a recording with a 48k samping rate can only accurately reproduce an audio signal that's less than 24k. The reason is that you need to take more than two samples of a waveform to determine its frequency and amplitude.
Of course, nobody can hear a sound with a frequency over 24k anyway (or even over 20k, or for many people, over something more in the 12k-16k range).
So ... possible answers to "does a sampling rate over 44.1 or 48 do any good?:
- Possibly, because (as already mentioned above), though no one can hear a super-20k tone standing alone, when combined with audible frequencies, the super-20k content somehow affects the hearer's preception of the audible range. Further notes: (a) this is, at best, extremely subtle, (b) this is, at worst, non-existent, as it seems inconsistent with how the human ear actually physically works.
- Possibly, because it allows you to move the anti-aliasing filter higher. More explanation: if you want to record at, say, 48k, you ideally should use a brick-wall low-pass filter than cuts off everything above 20k or so. Allowing higher frequency content than you can accurately represent can result in "aliasing," or the appearance of spurious lower-frequency signals in the audible range. Of course, there's no such thing as a brick-wall low-pass filter: any real-world filter will have some imperfections. Depending on the design, it will likely cut frequencies will below the intended cut-off frequency (remember that one octave below 20k is 10k), or "ring" near the cut-off frequency, or otherwise distort or affect the spectral content. Move the filter up to 40k, and you've got an entire octave above the highest possible audio frequency you care about.
- It doesn't make any difference that's audible to a "blind" ear, but if you tell people they're listening to a "better" 96k recording, it'll sound better to them merely because of that. Yes, this is nothing but a placebo effect ... but placebos do, in fact, actually work.