>> Given the weight and cost of Gore-Tex
I think Jacket 1 also includes Propore (unless I am mistaken). In which case, it is both cheap and light. Not quite as light as a really light poncho, but a poncho can't double as bug gear. But of course, a jacket can't double as a tarp.
Speaking of which, I know for myself, the main reason I use a tent is because of bugs, not foul weather. I could probably get by just fine with a tarp if I was only concerned about rain. But in the summer in the Northwest, bugs are a much bigger nuisance. A lot of the tarptents have weights that are close (if not lighter) than a tarp/bivy combination. Likewise, a lot of the double walled, or at least hybrid walled tents are lighter than the average single walled tents (e. g. Refuge X).
In that regard, the use of tents is similar to the use of canister stove. As the stoves have gotten lighter and more efficient, the difference has shrunk. There is nothing in here about the number of people on a typical trip, but I imagine there is a correspondence there as well. Go out for a week long trip with a couple friends and a canister stove is probably lighter (for the group). That being said, I agree with you, I think that is the most surprising part of this survey. I personally think canister stoves are a bigger hassle, since I have to figure out which canister to bring (how much is left, etc.). But once I start cooking, they are much, much easier.
I would imagine there is a strong correspondence between roughness of terrain and pole usage. The Northwest has a lot of very steep trails. California has its share, even though it has a lot more smooth ones. I think all it takes is one long steep section (especially going down) for folks to want to bring the poles. The fact that trekking poles double as tent poles (very strong ones at that) may bump the numbers as well.