I agree. It is a handy catch phrase that describes a real phenomenon. I tend to think in terms of variance. Programmer A is 3 standard deviations 'better' than programmer B (again, no mathematical rigor implied!!!).
Think of it in this way. Most of us are smart people, and learned relativity in high school or college. Those that didn't, could have. It ain't that hard. But how many could have discovered relativity at that time in history? None of us, I suspect. Put it how you want, Einstein is a 10x, he is 6std outside the mean, or whatever.
Same sort of things in software in my experience. If you have something really hard to do at work, you know who to give it to, right? You give it to (say) Jessica, who will come back in 3 days not only with it complete, but with all the ambiguities in the spec fixed, with 4 enhancements that you never thought of, documentation, and a framework that lets others in the company extend the functionality into other company products.
Or, you could give it to Jacob, who will need to be prodded for status updates week after week, and he'll eventually 'deliver' 10x the number of lines of code (hence just as productive by SLOC estimates!) for a substandard solution that is unreadable and fails on all the edge cases.
I call that 10x, without worrying about the math or quantitative part.
To anyone that disagrees, why all the hand wringing about hiring? Just hire anyone that crosses your door, they will be fine, right?