To answer your question Francois, I do think it is important for this particular piece to be performed by a human. Yes, in general it calls for an extremely precise tempo (quarter = 59.225 bpm), but aside from that I think much is missing if you were to have this done on via computer. Even a metronomoe would have stifled the piece, I think.
When I did a professional recording, I debating quite a bit about whether I should have an iPod with a metronome track so that everything was exactly even concerning pacing. (This wouldn't have been an option when the piece was written in 1971, of course. In fact, I don't know how difficult it would be to even get a beat track at exactly that tempo.) In practice, though, I didn't like how I played it with the metronome clicking in my head. So much of my attention was drawn to the beat-to-beat level that I lost something in performance. Thankfully, my producer had more faith in me than I did, and really encouraged me to try without. I ended up being much more pleased with the musical outcome, and was even able to nail it at exactly an hour for the recording.
Now, I still tried to keep a precisely even tempo, but that doesn't mean that I didn't (try to) do quite a bit in terms of shaping line or creating different tone qualities for different section. There was a lot of thought and work that went into the professional recording that I do think would be lost if it were done via computer.
That being said, I know that there are many composers who are very successful using electronics (sometimes combined with live players), but for this particular piece, I think much would be lost, and for the most part I think those that were intended to be performed are in the same boat.
Thanks for your interest!
(You can stream the CD, which is both a better performance and a much higher-quality sound - http://recordings.irritablehedgehog.com/album/tom-johnson-an-hour-for-piano?permalink