"Roughly the right amount of weight" may have been a miswording on my part - they didn't provide any calculation of what would have been the ideal Bayesian weight to put on your own opinion, as compared to the weight the participants put. However, there was a consensus effect, and the subjects were relatively accurate in predicting how others would behave. I do admit that my grasp of statistics isn't the strongest in the world, so I had to go by what the authors verbally reported.

Judges' beliefs that others responded the same way they do was positively, not negatively, related to accuracy — whether this relationship was evaluated within people across people within items, or across people across items. In addition, in the across people across items analysis (who is more accurate than whom?), optimal weighting of own response was generally positive, which we interpreted as contrary to the assertion that people "overweight" their own response.

As for the third study - well, it depends on how you interpret the availability heuristic. It is, AFAIK, true that e.g. biased reporting in the media will throw off people's conceptions of what events are the most likely. But one probably wouldn't be too far from the truth if they said that in that case, the brain is still computing relative frequencies correctly, given the information at hand - it's just that the media reporting is biased. The claim that there are some types of important information for which the mind has particular difficulty assessing relative frequencies correctly, though, doesn't seem to be as supported as is sometimes claimed.