If hashing power centralized (like if BFL plugged in all their preorders) people would get weary of the 51% attack and the exchange rate would drop. Right now it seems like there's a lot of uninformed people jumping on the bitcoin bandwagon so I doubt that would actually happen at this point in time. AVALON said their plan was to mine with what they turned into batch 3, but ended up selling them because of other companies lack of delivery. If they had done that they'd have have a significant amount of the network's power. Basically for these companies to succeed they need to sell units to distribute the hashing power or everyone will bail on bitcoin leaving them with a bunch of expensive paperweights. They need to think longterm profits. I think they'll all probably keep their own mining farms, but they need to make sure the rest of the network has a reasonable amount as well.