For the same reason that the elderly will call their web browser "the Googles", children will also tend to think of the first implementation of a concept they find as the definitive one. The idea will never occur to them that there's any other Minecraft server than Bob's Private MineCraft Capitalism Extravaganza that their friend introduced them to and plays on.
Children aren't smart, this much is known. This is fighting the symptom, not the cause. The real issue is that children who can't spend their money responsibly shouldn't have that money in the first place. If we go by the assumption that a child won't know when they're paying for a legitimate product or being exploited then why give them any money? If they don't spend it on a pay-to-win server then they'll spend it somewhere else and be "exploited" just as much, possibly on an iPhone game or something. If I give my child $1000 and they blow it on a Minecraft server then that's my fault for giving them that much money, not theirs. Children shouldn't be given that much disposable income if they can't use it properly. Punishing server hosts for the mistakes of poor parenting is not the right solution.
As chc said, I wouldn't apply the same reasoning to elderly people. Also, the issue that most people were bringing up was that children specifically were being exploited, so the point is moot.
I think that's besides the point. This contract isn't "about the kids", it's about all Minecraft players and server administrators. If a server administrator feels they need to, or want to charge for some item or plugin, they should have the freedom to do so...
...after all, they aren't obligated to run a minecraft server in the first place, and if the only thing keeping the lights on is selling some in-game item, let it be.
