Armour Penetration on gear was not desirable enough. Thought Blizzard. So, they went ahead and increased the amount of actual ArP per ArP-rating by 25%. It became more accessible, and players were able to try out extremes. And all of a sudden discovered, that it’s a superior stat for some (most?) physical-DPS specs. So, for those specs, stacking ArP up to (conditional) 100% became the widely accepted winning strategy. As Ghostcrawler puts it, people started “tossing aside” gear pieces without ArP no matter what else they provided, as ArP became a stat that “trumps all other stats”. A situation GC/Blizz do not like to see.
Thus, the announced change for 3.2.2 is that ArP-from-ArP-rating is going to be reduced back by 15% – slightly lower than the middle between the old and the current value. How did the player base of the affected specs react? Are they intending to take a more balanced approach now? Nope. Word of mouth is “you still need to reach the same ArP numbers, you’ll just need more rating to accomplish that”. So, non-ArP gear will be tossed aside even more, because people will thirst for even more ArP-rating to reach the soft cap.
What went wrong? Well, ArP still “trumps all other stats”. Apparently it always did, players were just not easily able to test it out under real-raid conditions. Now that they were, and found its upside, they’re not ready to back off from it again, since it’s not actually being changed. That’s the point. ArP itself was not changed. It was neither made “more desirable” before, nor is is about to be made “less desirable” now. The product is the same, all Blizzard is tinkering with is the price.
Instead of the intended balancing, what was in fact pulled off is marketing. The ArP Soft Drink wasn’t selling well enough, so they gave away a truckload of free cans, and once people got hooked to it, yanked the price up. It’s not at all what they wanted to do, but it’s what they accomplished. Oops! Next thing to expect: harsh DR and hard caps on ArP. And forum QQ.