Couple of things to keep in mind:
1.) Having been an off and on customer of USAA for the ~20 years I've been married, they've provided some good deals and service that I have been surprised by. This wasn't the first time. Maybe this is just another one of those USAA things like the time I was pleasantly surprised by our new roof after Ike.
2.) We have multiple houses, multiple vehicles, and a ton of other stuff to insure in addition to the normal homeowners insurance. Like I said, my wife took on our insurance consolidation and bundling as project to be tackled. I am quite certain there are some volume discounts and economies of scale floating around in there that are tied to the amount of other stuff being insured, along with some haggling from Mrs CL the attorney.
3.) As much as I don't understand USAA in a good way, my experience with the insurance industry in general is equally hard to understand in a bad way. That industry is infuriating to me with the scams they run on people ("That's not a flood, it's surface water... and you're not covered for it!") and the way they just pop up out of the blue and ask for more money (It's called a "premium audit"). I'm not surprised that one company would be so different than another. Definitely shop around more.
OK that was three things.