1) the model car companies today are extraordinarily short-staffed vs even ten years ago, much less decades ago. There just simply isn't time or manpower for them to consistently maintain a view of the boards and respond. Stated another way, if there are only so many hours in a day, I'd rather see them working on new kits for us, than shuttling that aside to man the message boards.
2) companies in general (not so much the model companies specifically) have sometimes found that when they attempt to respond to criticism on message boards, it turns into a very negative situation. E.G. the situation worsens rather than resolves itself. They sometimes get better results by responding to individual messages rather than posts on a publicly-accessible message site.
Having worked with Round2 for the last few years, I have to say you are absolutely bang-on, Tim....especially on the first point.
I also agree re the guesswork and rampant speculation that results when people on message boards start trying to fill in the blanks when little tidbits of information are released. The various rumors that were generated when plans for a '71 Demon were announced are a prime example.