Why not (other) researchers doing some (other) study on the efectiveness of such obvious attacks? You know, active study, instead of passive.

If some researchers were trying to intercept my emails as a part of some active study, I would still consider it to be a criminal activity.

If the NSA were trying to intercept my emails without a warrant, I would still consider it to be a criminal activity.

Warrants? They have plenty of NSLs and even executive orders at hand.

"By law, NSLs can request only non-content information, for example, transactional records and phone numbers dialed." - http://en.wikipedia.org/wiki/National_security_letter

Executive orders are also subject to law. An executive order would not have made Nixon's wiretaps legal, for example.