I have personally started this trend sometime ago, making the opener with Kart's Community Motivator achievement. Dejanira then followed for her consistency in finding typos.
Today, as I was reading through the suggestions topic, as BigTea has "spammed" all over the place there, I realized that this guy needed to be rewarded somehow for all his contributions. Mostly because he is also new which adds importance to his suggestions as it is harder for newcomers. Then I thought that Haron also deserves the same reward. So I have decided to reward them both in a similar way.
Then I thought that I should reward a couple of people more, who have helped us greatly in the past, namely Skyhawk and Sir Henry Morgan for their aid in the Bounties and Bank features respectively.
So, we designed an administration tool to add these rewards and any future rewards easily.
Once the tool was ready (in short time, really) then I thought to reward some more people that deserve some recognition for their special support these years in game design. This is where we thought to also add the achievements to Global Events log.
Once this has been made, I thought to flood it a bit as it looked empty so I checked up on the forums for guys and gals who have been historically very helpful in the game design mainly. I had to put some strict criteria there or else I would need to give many rewards as participation has generally been very good.
So these rewards have eventually been given out to people who have stood out from the rest. It does not mean that if you got no achievement that you have not been helpful. Do not focus at the negative side. Focus at the positive side which is that the people who got it, have done this extra something.
Special Achievements will become a tradition from now on. However, they will be very spontaneous and rare.