I'll go ahead and stop you right there Phillip Have you ever seen anything that has lead you to believe there is even professional courtesy for one another among the big dogs, let alone actual collusion? That is a massive assumption, and one that I do not believe to be true. There will always be the company that thinks that they will be better, more efficient, more dense & finished sooner, and would only be helping their competitors by putting a leash on their own hashrate.
It's the prisoner's dilemma, that which is best for all as a whole will often not be the decision made by the individuals. Network hashrate has been increasing almost continuously, and it takes many more PH/s at every adjustment to maintain your chunk of the revenue stream. If what you said was true, what incentive would they have for developing new miners as quickly as possible with higher density? I would bet that the amount of money saved on electricity over an entire year (if in-house hashrate were to remain flat) would not make up the amount of money required to develop and build a new generation chip & miner. They do it because A) they feel they need to push it further in order to survive and B) they want to get an edge on competitors and drive the smaller ones out of business, freeing up more revenue from themselves. Consider this, if they had kept hashrate constant over the past year by colluding, AMT/BFL hardware would still be profitable and competing with them on the network today. By driving the hashrate higher, they knock more people out of the runnings, and take a higher percentage for themselves (even if it comes at a cost).
And there is the truth Phil, that's what they all believe. Look at the bullshit PR and fluff that goes on by the manufacturers (look at Bitfury's Twitter page for some examples). It's all secrecy and speculation, to try to discourage your competitors from further development. (read: the exact opposite of collusion)
If you believe that KNC, Bitfury, Innosilicon, SP-Tech and Bitmain have a handshake agreement to keep the network flat, I'm not sure what to tell you except look at the fact that the network hashrate has doubled in the past year (which has been mild compared to the prior year). The reason it has been increasingly more slowly recently is due to the fact that many of the competitors have been knocked out of the game (due to the fact that they keep driving it higher), or were in between generations.
i think collusion is a strong word, but i also have a feel that hash rate is being "managed" through periodic large % switching on and off-you can see it in graphs.
most likely large miners analyze the hash rate and see when it is the most beneficial to switch a largish % off (in the last few days before adjustment, of course) and when to switch it back on-in the beginning of the period, of course. Or, maybe nobody does anything proactive, and it is just statistical fluctuations.