At the same time, I'm not sure they could have clearly addressed any of the specific criticisms in the open letter, for fear of prematurely revealing company strategies and plans. (And don't give me a line about how companies need to be more open; every company with any competition has to be ever vigilant about that, for competitive and other reasons.) Note also that they didn't claim any of the specific criticisms were invalid.
(Well, actually maybe they could have toned down the FUD on the source in the first paragraph a bit. But I think they had to include some of it, frankly; unless/until a RIM exec publicly claims responsibility, none of us know for sure it's from who it claims it is.)