[donh]

Newton's laws haven't been replaced by Einstein's Theory of Relativity - they are subsets of the same that hold true for a given reference frame.

This statement reeks. Newton's and Einstein's universes imply two radically different, generally contradictory "reference frames". We hang onto Newton's laws because they are computationally cheap approximations that will serve in most low-cost earthbound circumstances, not because they constitute a proper subset of Einstein's laws.

[Old_Mil]

We hang onto Newton's laws because they are computationally cheap approximations that will serve in most low-cost earthbound circumstances, not because they constitute a proper subset of Einstein's laws.

You're contradicting yourself. If they weren't an adequate approximation of a subset of Einstein's Laws for the reference frame of Earth, holding on to them as a low-cost computational approximations would be pointless.