The problem is everyone sees the word classified and assumes it must be important, that is not always the case. Just because it is classified does not mean that reveling it would have an impact on U.S. national security. For example, the number of rolls of toilet paper bought for a unit every month maybe classified, due to the fact you could potentially determine unit size and strength from the number. However, it has no impact on the overall National Security of the U.S.
The fact that he is a PFC. means nothing either everyone in the military has the equivalent of a secret clearance it does not mean they have access to anything of importance though. It is just poor journalism and over excitement by Wikileaks in thinking, they have something valuable because it is stamped classified. Nothing of real importance was released in regards to national security, but it sure has helped to feed the ego of someone that seems to crave the spotlight.