JB,
Very useful. I may be able to shed a little light here. I was in a Head Quarters when FoI became an issue to us. The rule was to destroy anything we didn't actually need, including documents and emails, on the grounds that if we didn't have them we couldn't release them to an FoI requester.
While I don't think our part of the organization was trying to evade the Act, it was clear to me (assuming I read the signals correctly) that the Centre was very nervous about it. Instructions about how long we had to respond and under what circumstances we could legitimately decline were very clear.
A view I have held for many years is that it's very easy to think of the RAF of the MoD as "them". There is no corporate "them". It's a bunch of people in a job for a couple of years in most cases. Especially those that have to deal with FoI requests. Mostly those desk officers scrabble around to find an answer, but often feel uncomfortable being the one to let something slip - often not fully understanding the politics/sensitivity of the issue. So they revert to safe mode and pull out one of the standard responses.
All the above is not to say that there a many pieces of information that the MoD would rather keep to themselves - PRESUMABLY, but I cannot state that for certain.
Fortunately, I don't have to deal with that sort of thing any more.
Courtney