As someone else pointed out Cox's example was not a tautology. To say that something is a tautology is to say that it is true for formal reasons and not contingent upon empirical facts.
Some equations are contradictions and so are false for formal reasons.
Mathematics is trivial in that it makes no empirical claims or is consistent with any possible set of empirical facts. John Stuart Mill would agree with you. He thinks that 2 plus 2 is 4 is an empirical fact illustrated by adding 2 marbles to 2 more etc. But getting 1 drop from adding 2 drops to 2 others doesn't refute the proposition that 2 plus 2 is 4 or just show it is highly probable. At least I am as firm on that as Mark is on the oil crisis.