That's not entirely accurate. Blizz doesn't usually take away anything your class/level was legitimately able to acquire, like achievements/items. The types of thing they like to take out of your hands are the items/achievements your class/level never should have been able to get in the first place. Some examples were the Northrend grey 2H sword that had no req level when WotLK launched so level 1's were using an item with like 200 dps on in. Another example were dungeon achievements like say Dire Mall at 1. Back in the day you would stand by the portal entrance and have a Hunter kite a mob to you, FD then it would kill you. You then rez'd on the other side of the portal and blam were inside the instance. You had access to Run Tum Tuber Surprise cooking patt, the world event achievement for looting the rose and the achievement for completing the instance. It's those kind of thing Blizz usually takes away, not items acquired by normal means meant for your class/level (usually).
That said, yes it's going to piss off far more than just twinks if they remove the AGM from the game as said before it is 2 achievements for any level.
There is one area Blizz could hurt twinks and would cause a huge riot if they did and that's rep. At current most of the rep grinding to be had in Classic/Outlands can ONLY be completed through exalted by following a high level toon while dead. Obviously Blizz is aware that you still gain rep while in spirit form, and if they really cared they could just remove that and ouch for a ton of people.