My guess, and this is just a guess, is that a lot of distributors assumed that they would get the same quota of machines they usually do, and sold on that basis.
When their actual allotment was given to them (why this is done a week later, I don't know), it's seen as a 'cut'.
Hell, some distributors are taking pre-orders on Star Trek, and have been for months. How do they know how many of those they have to sell?