IMO real-time has a perfectly good definition. It means a system which doesn't miss any of it's deadlines. So an ABS system *has* to update the current in the solenoids every xms +/-yus - if it meets that, it's real-time target is met. A human oriented system may have to respond within 10ms to a keypress so as not to appear sluggish. Real-time has no numerical value, it's about meeting timing specifications. Then there's hard-real-time and soft-real-time - which is about how badly things go wrong *if* you miss the deadline...

Jaguar has had drive by wire systems for a while now where there actually isn't any physical linkage between the wheel and the tires.

Between the *wheel* and the *tires* - surely there's something there :) If you mean no connection between the "hand wheel" and the "road wheels+tires", then I seriously doubt it. Citation?