I suppose those continue working fine in very local systems (contained in a ball of a few light-seconds radius) whose components move at speeds where relativistic effects can be discarded. Drop those constraints and you also need to drop even system-local globality because of relativity.
You _could_ introduce the One True Lamport Clock, and as long as you're in its light cone you can get global syncronization, but that comes at the cost of having to learn a lot about patience.
