it's perfectly true that Goretex won't work if there's a higher temperature on the outside (eg heated grips) but the science of the article isn't correct. Goretex relies on a higher temperature on the inside than on the outside of the garment to drive the moisture through the membrane, it's that simple. It's not to do with the relative humidity levels inside to out.
Even if it's more humid outside the garment, the moisture will be forced through from the side that is warmer, usually the side against the skin. That's why the pockets on Goretex outdoor clothing won't remain dry if they're a second layer of Goretex fabric simply stitched over the Goretex jacket - sometimes they'll even hold puddles of water in heavy rain. There's no heat in the pocket itself to make the outer membrane work.
The same misinformation with the t-shirt example, the reason the cotton gets wet is because it's brilliant at absorbing moisture - body moisture from the inside, not rain from the outside! The cotton will absorb moisture at a higher rate than the heat differential can drive it through the membrane, added to that the fact that the cotton will drop in temperature as it becomes moist and the effectiveness of the membrane is reduced even further.
