Few last points before I duck out of this conversation for awhile...
There are international accounting standards (see: http://en.wikipedia.org/wiki/International_Accounting_Standards_Board). It's not necessary that all organizations follow them to the letter, obviously, because not all nations (including the United States) accept them. The point is, I'm sure, that in order for the WMF to achieve the points laid out in the Board letter, they will need to see certain types of information from the chapters. To have confidence in that information, some common understanding of how reports are developed will have to be agreed upon.
I don't have the background on the Board's decision necessary to understand why they chose the particular timing they did. If it were me, knowing only what I know, I would have deferred the effect of the change until the next fundraiser. But, that carries risks - if they were informed of a material problem and chose to defer for a year, they could incur some serious liability. I believe they see the Wikimedia movement as an international endeavor, and the chapters as an integral part of it, and I remain convinced that the Board members have the best interests of the Foundation and the movement at heart.
Having said that, Assume Good Faith is not how corporations with lots of money protect themselves. It's a good principle when interacting with people, but corporations (for profit or otherwise) need to establish controls based on the potential for bad actors. It's not about distrusting partners, its about fulfilling a fiduciary duty of care for the corporation that will survive changes in personnel and circumstance.
Finally, the WMF certainly does have an obligation to meet the expectations of the community in many areas of concern. That doesn't mean they can or should reveal every detail, nor does it mean it will always successfully meet the expectations of every individual or even the community as a whole. Perhaps Theo's experience with this list is different than mine, but after 4 years of subscribing I can't think of anyone who doesn't believe the Foundation is responsible to the Wikimedia community.
Nathan