Because of season three's stopping point - roughly ¾ of the way into George R.R. Martin's third Ice and Fire novel, “A Storm of Swords” -- season four seems likely to continue on a consistent path in terms of core characters and events. The future grows muddier when it comes to the next two books though: “A Feast for Crows,” and “A Dance With Dragons,” the former of which omits such characters as Tyrion, Jon and Daenerys, as well as introducing new protagonists and plot-lines. But as writer/exec-producer David Benioff and his team realized, Book Five overlaps with Book Four's timeline, and so the season afterwards will blend the two for its material.
He also put forward the likely notion of cutting down on excess. “The series has already reached a point where there are so many characters -- particularly in season three… we run the risk of bursting at the seams as we try to cram every single subplot and all the various characters and it becomes impossible on a budgetary level and it becomes impossible on an episode-basis to jump around every few minutes to 30 different characters and locations. We don't want to do that, and recognize that as a real risk and we will take steps not to fall into that trap.”
There's the point too that Book Four remains one of Martin's most tepidly received efforts -- a swell of negative criticism that could disappear with the TV adaptation's narrative swirl of the next two books. Also, with actions like this, combined with Martin's notoriously-delayed releases (his sixth, “The Winds of Winter,” is currently being written), the possibility of the HBO show catching up with the author's has been raised, but he isn't worried.
“I think the odds against that happening are very long,” Martin said. “I still have a lead of several gigantic books. If they include everything in the books, I don't think they're going to catch up with me. If they do, we'll have some interesting discussions.” [via EW]