I suspect noonehomer's correct in part and that the chareidim don't actually believe everything that Username says.

Also, I don't think it's true they don't let anyone go to the army (or at least it didn't use to be), just that it's discouraged.

If anyone's interested in my own thoughts, I posted them in a comment here. Just look for the comment by iarwain. Sorry, you may need to understand some hebrew terms to understand it. But then again, you'll need to understand hebrew terms to read Username's comment as well.