Most of my flats are glass or pieces of wire worming their way into the tube. I never get pinch flats. Both seem to be a matter of how thick the rubber is on the tire in my experience. That may have to do with the kinds of tires I use and the kinds of conditions I ride in - perhaps its not universal. If you feel a new tire and a worn tire, there's a pretty significant difference in thickness - a new tire might be double the thickness of a worn tire. Right now, my tires have tiny cuts all over them, but none of those cuts have resulted in anything making it through to the tube... yet.

I haven't noticed a seasonal trend. Most of my miles are commuting. I ride less in the rain, but I ride the same miles year round.