I think eric that you are mistaking complexity for unpredictability.A programmed system is deterministic in that if you know all the details of the system and you know when external and internal events occur then you can predict the outcome, which is why simulators work.Your argument only applies to non-deterministic systems where you can know all the details of the system and you can know when events occur but the outcome cannot be predicted which is not how digital systems work,I agree that there are parts of digital systems which are inherantly non-deterministic such as metatstable inputs but good system design allows us to ignore those effects because we know that in a properly designed system the chances of for example a metastable input crashing a fly by wire plane are so slim that nobody says we cannot use computers to fly planes because there is a 100 billion to one chance that they might fail because of a dodgy input.