the rubber in a tube has a limit to how much it can stretch before it tears, much like a baloon. if you are using tubes that are much too small filling the tyre will put them closer to this point, making it theoretically easier to puncture the tube. thats the science behind it anyway.
the latex tubes mentioned leak not because they are thin (they are actually a relatively thick tube for their weight, I envisioned them being like a franga for your wheel, lol, pulled them out and they are thick like a dh tube) but because latex is not completely air tight, the air seeps through the latex. reason whey they are claimed to reduce punctures, is because they stretch so well (Ithink their marketing BS says they stretch 7X better than butyl) and are not at the point where they will tear if they get pierced by some thing sharp. pinch flat resistance is really along the same lines but without the piercing object, instead view the area of tube being squashed between the rim and tyre as being stretched out very thin (to the point of tearing).
My latex tubes havent had a puncture yet, 4 months in. im sold on them. but thats in more of a AM application, however my next tubes in my DH bike will be latex, to see how they go.