Brian: the problem was not publisher's deadlines - George missed those a long time ago - but book size.
AFFC was already longer in MS form than ASOS. That meant that it was certain to come out as two, possibly three, paperbacks (and a truly MASSIVE hb).
Rather than do this, George revisited the structure of the series. He preferred to issue two books rather than one that would inevitably be split. Seems fair enough to me. Fairer to the fans, and to the story. (He doesn't say, but he implies, that the alternative (split pb) was the publisher's choice.)
What does worry me about this slightly is that this was a problem he was already aware of when he started. He aimed to make AFFC roughly the length of ACOK. Instead it wound up as the longest book so far. This suggests a degree of lost control.
We all assumed that six books meant seven all along (even Parris). Now, we have seven. If that's not to become eight, George needs to get a firmer grip on the story, what to tell and what to leave out. (Not so firm a grip as to crush it, mind.) I have faith that he can do this, but it does seem to be giving him trouble.
The good news is that ADWD will follow swiftly on the heels of AFFC, since it is half written already.
(Many of us are now in the peculiar position of having read preview chapters from book 5 before book 4 is released.)
