Sequencer wrote:But that's not really my point - it is useful - the ability to 'print' an exact rendition of anything in the digital world..
But is it really 'useful' in the context of a musical instrument? The chances are you're going to modify the source sound with effects processes anyway. But even if not, the degradation involved in passing through a D-A-D process is so vanishingly small I can guarantee you will not hear it, and you'd be hard-pressed to measure it.
Analogue connections are universal. Balanced analogue connections are interference and ground-loop resistant. And analogue is also sample-rate agnostic.
In a keyboard, digital I/O is a pain from the practical, operational and engineering points of view.
To do a digital output correctly, you need a very high quality internal clock, and the ability to synchronise to an external clock input, and the ability to work at different sample rates... All of which makes the design of the keyboard's digital sound generation a lot more complicated and therefore expensive.
And if you don't provide external clocking and alternative sample rates you compromise the usability of the digital output...
So given that there are no real practical benefits, it's a lot easier just to not bother with a digital output. Spend the money on much more useful balanced analogue outputs instead.