I think its just a way to condition them to the idea that the government can demand service of them and they must comply.
Or... maybe it's a way to get them out to do something nice for the community in the hopes that they will enjoy the experience and continue to do such things out of their own volition later in life. I'm sorry to break this to you, but politicians are human beings, not emotionless robots who exist solely to break the wills of their subjects.
Not to say that I agree with requiring community service before graduating, but I think you're being a wee bit too paranoid there.