There's been more written about this than about abortion, but here are some thoughts:
--It's probably not coincidence. I used to keep track of flats, and one summer I averaged one every 30 miles (lots of thorns here), but they were evenly distributed front and rear.
--Do you know where on the tube the punctures are occurring? Inside by the rim or outside by the tire? If they're near each other, that gives you a clue. If you always mount the tire with its label aligned with the valve, then when you find the hole in the tube, you'll know where to look on the tire for the sharp thing.
--If the punctures are on the rim side of the tube, recheck the spoke ends etc. CAREFULLY. A tiny burr can wear through.
--Also check around the valve hole in the rim for rough spots.
--Be sure the tire isn't holding a tiny glass shard or the tip of a thorn. Feel around the entire inside with a finger. Somebody already mentioned this, but it's important. I ran over a thorny branch one time and had nine flats before I got the last tip out of the casing.