When I heard 'im talk saturday (yay! still psyched about that) he explained that when he started to write the 4th book (now pushed back to fifth) after the gap, he turned out to be writing hundreds of pages of mainly flashback sequences, people sitting around saying "remember when xx happened". He couldn't manage to make the connection in a good way, so that's why he removed the 5 year gap in favor of aFfC. This, incidentally, also cost him 6 months of writing time which were ditched, which explains some of the lateness of the book.
[Note: Having solicited questions to ask GRRM, Jasper says he asked only one, concerning whether Sword of the Morning was a familial office or a unique epithet for Ser Arthur Dayne.]
GRRM: "There have been other Swords of the Morning."