I would disagree with Roberts that just "the immense accumulation of and attention to trivial details" are the reason for the success of WoT (I still don't know if Balwer is left-handed or right-handed!! ). I also seriously doubt that any fan cares much about the "the shift into increasingly obviously sexualised territory", besides that it's simply a logical consequence of the new relationships between some characters in the series. But certainly no one is that thrilled if a low-cut dress is mentioned (except for Roberts himself apparently..).

Similar to fionwe1987, I think the secret of success is rather that the tapestry or pattern, which RJ has woven in his story - with all the interlinked characters, plot-lines, prophecies, riddles, magic, themes, motifs, etc. - encourages people to speculate and discuss, especially since many things seem familiar from well known myths like King Arthur. Plus, due to the time spend on the various characters or cultures, the WoT world seems especially alive and the readers want to know what happens to them; it's certainly also some kind of escapism to dive into the breathing WoT world. For this reasons, you want to read along to get new informations, but naturally also interesting resolutions. Finally I think the prose isn't that bad and definitely very accessible. In my view, one can really compare WoT in this respect with a successful "fantasy" TV series like Lost, which basically uses similar techniques to fascinate the audience for about six seasons. Of course, some fans are eventually bored or confused by it and scream for all the resolutions before the actual end, but the majority is still thrilled.