@Capt. Bloggs, aterpster:
I think you're being a bit cynical there, to be honest.
In this case I don't think it's a case of politics as much as a case of "once bitten, twice shy".
If you cast your mind back to another 1979 accident - namely AA191 - you may recall that an unprecedented level of media interest and pressure regarding the case caused the NTSB to have their lead investigator hold a press conference which identified a broken engine mounting bolt as the primary causal factor of the accident before their metallurgist had been given a chance to inspect it. Before long, it became apparent that the bolt had fractured on ground contact, which caused the agency considerable public embarrassment when they had to make another announcement that they were wrong.
It's therefore entirely unsurprising that they henceforth put much stricter rules and guidelines in place when it came to releasing information to the public - particularly prematurely.
What we seem to have in this case is the pilots' union making a premature public statement and the airline representative rebutting that statement - which both parties had agreed not to do before the official report was published. The risk of this kind of premature release of information undermining the credibility of the investigation is very real, as AA191 proved, and for better or worse, I believe the NTSB are justified in the sanctions they gave those parties.