Like the comic adaption the original book had the scenes with biggs (on Tatooine and on Yarvin). Additionally it had the Jabba the Hutt scenes in the hangar. (For I'm not completely sure if it was set in the hangar, but the two (Han and Jabba) met in this scene and Jabba was not described as a slug!
When the Special edition was released there was a new comic released. In this one the scenes with biggs on Tatooine were misseng, the Jabba scene was altered to a Jabba-slug scene and the Biggs scenes on Yarvin were in it again. As far as I recall the kissing scene between Luke and Leia was changed, too (short kiss before they swung over the gap on the death star). While in the OT-comic book Leia kisses Luke on his mouth she kisses him on the cheek in the SE-comic-adaption. (While the kiss in the film did not change.)
Why the book has not be changed when the SE was released I have no idea. Maybe it has to do with the problem that GL is not the true author of the book but Alan Dean Foster and so the book would have to be completely rewritten?