With all due respect, I think you're a little off here too (though obviously not anywhere near the level of some of the mouth breathers in this thread). DIPS are not merely predictive of ERA. They are also a measurement of a result set. The elements of that result set are deemed to be a more direct measure of things the pitcher can control.
If this weren't the case, there would be no argument to use FIP in WAR. WAR is simply a valuation framework, an economic tool, for translating a result set into value in a more tangible form.
If we want prediction, we use a projection system. While they all use many of the same principles that went into the creation of FIP, xFIP, is a different mechanism.