I'm going to dissect some well-known facts. If you disagree, or want to add one of your own, the e-mailbox is waiting.
Slack wet guy ropes
Those still using guy ropes, especially nylon ones know if you set up a tent, or most commonly a flysheet with longish nylon guys in the dry, after the downpour starts, and all is soggy you have to make an unpleasant trip outdoors and shorten the guys like mad, since the main fly, tent or both are hanging slack.
Nylon in fine-cord form does absorb water right into the plastic, which then softens the material and makes it easier to stretch. There is thus nothing wrong with the half-truth, since this will cause the guys to slacken.
What has been forgotten is that a nylon flysheet weighs at least twice as much soaking wet as it does dry. The extra weight greatly increases the load on the guys, which being elastic simply stretch. I would guess two-thirds of the 'slack guy effect' is due to the load weight increase rather than the change in properties of a wet rope.
The marvellous double-skin tent
Most modern tents have a waterproof close-fitting flysheet with a water-permeable or porous inner. When the weather is dry and cold, this permits moisture to exit through the inner wall, allowing the tent doors to be kept closed. This makes for a snug and reasonably dry tent, although really cold nights will of course allow condensing breath to freeze on the tent inner.
Most of us can remember the waterproof nylon ridge tent with no flysheet, closing it up at night to cut the draughts, and having condensation running everywhere inside by morning. Much of this can be prevented by leaving the end window and doors open, keeping the mesh zipped up to exclude mosquitos and snakes. A steady draught moves inside the tent all night, and most of the condensation troubles are removed. If you pitch a fly over a waterproof tent, despite free air circulation between the two, the fly normally covers with heavy dew or frost at night, while the inner remains dry. Sleeping in the draught under the tent/fly is cooler but drier than a double-skin tent.
Real camping and personal survival revolves round the unforecast events once every few years when the weather turns unexpectedly nasty. Storm-force winds can rip a flysheet, and if heavy rain is also on the agenda this can leave you sitting in a porous nylon inner getting wetter by the minute wondering what to do until morning. If the outer fly destructs on a proofed-inner ridge tent, you can peg down the walls to cut the windage on the main tent if required, and wait for daylight in a damp but still waterproof tent.
The half-truth in this case is that a double skin permeable-inner tent is superior. In good weather perhaps, but you are relying on both the outer and the inner not to fail if you want to stay alive. A tent with a waterproof outer and a waterproof inner will still protect you if either the outer or the inner is destroyed.