The trouble with just centering the wheel as you tighten the QR skewer is that the vertical loads are taken solely by the grip of the skewer instead of the axle resting in the DO. If you don't get it tight enough it could slip if you hit a bump hard enough. On the other hand, I've see hubs where when the bearings were adjusted "just right" I could tighten the skewer so much that the bearings would thicken up. That argues for not making the skewer as tight as you can get it. So how would you find the right amount?

Here is another possible cause. Twice I've had a LBS dweeb put an axle in a vise and tighten it enough to ovalize the end. The result was that when I put it in the DO it might or might not skew the wheel, depending on how the axle happened to be rotated at that time. (Another symptom was the threads on the skewer would catch on the slightly flattened ends on the axle.) If you've reversed the wheel and it was still offset the same way then this isn't your problem. Unless your axle is damaged at both ends and you just happened to mount the wheel with the same effect. That's unlikely but if you or a PO or a LBS dweeb worked on your wheels, including a spare wheel you might have tried, then it is always possible. Replacing an axle is easy and relatively cheap.