The article talks about the issue of the math behind the attack/AC accuracy curve.
3rd Edition and 4th Edition both assumed you would have certain magical bonuses as weapons or armor at specific levels just to keep up with the math of the monsters at those levels as well. 5E ditches that so that you are no longer required to have those bonuses just to hit things or not get hit all the time.
Damage Immunity and Setting Scale
D&D in general assumes at least some magic, and some magical items. If you decide to go for a low magic setting, certain things change from "default" D&D play.
Consider the difference between a monster in an action movie vs. a monster in a horror movie - typically the monster in the horror movie is more dangerous just because no one has the knowledge or the tools to deal with it. In an action movie, 100s of werewolves might just be the 'average minion', but in a horror movie a single werewolf is an overwhelming threat.
If we look at fantasy, you can see in both Conan and Lord of the Rings several creatures are pretty nasty and the only answer is to run or find a rare magical way of defeating them.
If you decide to do low or no magic items, you either decide: a) those monsters don't really show up, b) those monsters are rare and a BIG deal, perhaps undefeatable in most circumstances, c) those monsters are frequent and humanity is living a scarce and marginal life trying avoid them.
Out the math, easy hacking
One thing that taking the math of the accuracy/AC curve out of magic weapons is that it becomes trivially easy to hack those damage immunity scales to your game. Instead of going "Ok, at level 3 it's a 1 AC I need to take off, but at level 22 it's 8 AC I need to cut down just to make this work..." you can just go, "Ok, it's damage resistant, rather than immune", "It takes only 1 point of damage per weapon die, that's it." etc.
You can scale it up or down or remove damage immunity altogether without having to do a lot of complicated math, especially with the diverging attack numbers of the different classes.
It'll be interesting to see how specifically they address this issue in the DMG, since it's been said that the goal of that book will be to give DM's the nitty gritty of design and options to modify their campaign.