I found an article of "Japanese airlines deny collusion on mail contract bids" on yesterday's Financial Times.
ANA said that they are extremely surprised to see the same bids, and they are determining their bid rate by careful analysis and research.
"Dango" is a traditional way of bid-rigging in Japan. Usually companies exchange information through industry groups before jointly determining the price and winner of each ear contract. Major "dango" usually occurred in bidding of public construction project. Big construction companies talk behind closed doors and win the bid in settled order and settled high price.
"Dango" could function only when all the companies follow the hidden contract, and I think this is based on very Japanese culture. Japanese tendency to follow the rule settled among the group is very strong.
Besides "Dango", many of Japanese dispositions could be explained by rice cultivation. Indeed, Rice is Rife.