Ah, I see, now I understand what the problem was.
Originally when I received the silverfish and ghast spawners (note, this was before the rules against them!) I placed them in the zoo. It turned out I had an excess. Too many animals were spawning. Once there are too many they start glitching through the walls and eventually escape. I do not have to explain why that would be an issue. I took serious security measures to prevent this from happening, including making the entire nether part of the zoo three layers thick. This was a lot of (invisible) extra work which only shows that I take spawner security quite serious. Ghasts can never escape from the zoo, even with all plug-ins off. Silverfish are harder to contain but can never escape that floor of the zoo.
I did not want to throw the excess spawners away because there have been A LOT of issues with spawners in the past and I wanted to keep these as backup for the zoo. Using them in a mob grinder would not have been fair to other players, so I didn't.
Putting them as spawners in a chest was not an option because, as we all know, when Bukkit gave out all spawners reverted to default (pig). I was doing maintenance in our mob grinder that day and half the spawners turned to pig. I did not want that to happen again.
Putting them as eggs in a chest was also not an option. I myself was the one who reported the spawner "duplication" bug. When I came with that knowledge to the staff, it was not unlikely that the turning-eggs-to-spawners plug-in would be decommissioned. In other words, eggs might become useless.
The only spawners we never had issues with, are spawners placed somewhere in the world. I took all possible security measures: the room was too small for ghasts to spawn; it was well-lit so silverfish could not spawn; it was in a protected area with spawning turned off; it was somewhere no one could reach or see it in the middle of nowhere.
I understand if you want to take these spawners away. But please, if the ghast and silverfish spawners in the zoo are ever destroyed for whatever inconceivable reason, I would like them to be replaced. Spawner plug-ins have had considerable issues.
I hope this long explanation will suffice, I am available for any follow up questions.
Last I would like to say that I often come to staff with often very serious bugs. I was the one who reported the Bukkit spawner-to-pigs issue and the tradecraft item stacking issue. I also reported the very bug for which I ironically ended up being banned for. Just earlier this week I reported a serious security bug to the staff.