[Note: The following is a brief excerpt from the owner of Clarkesworld Books, a particularly popular bookseller among ASoIaF fans due to his excellent service and his stock of hard-to-get GRRM novels and collections.]
After John left, I decided to drop by the signing tables since George R. R. Martin was scheduled. Much to my surprise, there was no one in line. I spoke to George for a couple of minutes and asked him if he would mind signing a small stack of A Feast for Crows for the store. Yes! I ran off, picked up the books, came back down, and there was still no one there. While signing, I asked George about the RRetrospective. He told me that a UK edition was in the works and that iBooks had wanted to do a two book version, but he refused. (good thing since iBooks just went chapter 11) He suggested that I bug Bill at Subterranean to do a second printing.
...
Oh and the reason for turning down a two volume edition was that the the whole point of the RRetrospective was to get everything in one book.