They've made digital doorbells that 'sound' 'like' actual doorbells, cell phones with ring tones that ring like the phone in a 1940's detective thriller, etc. Has anyone yet thought to make a digital clock that ticks like the real thing? Surely there are few more soothing sounds than the regular ticking of a clock. Veterinarians recommend wrapping one in a small blanket for kittens to help them sleep (reminds them of mommy's heartbeat, I guess).
Thing is, like all the other senses, sound is one of those things that's very difficult to fool - we pick up on ersatz sounds very easily. Even if you don't pay attention to such things, you might hear a digital piano in a song - no matter how well done - and think to yourself that it sounds a little off. I can just imagine that what we think of as a regular, unchanging sound - the clock's inflexible up/down ticking rhythm - is actually made up of a million tiny variants in tone. Each tick and every tock as individual as snowflakes. The digital version would just be one tick, and one tock, cycled over and over and over again, and we'd know it's wrong, because it would never change - whereas the real world is constantly stumbling over itself.