But once George wasn't the sole contributor to the SW universe, it all became very complicated. Hence why there were a bunch of people at Lucasfilm who were gatekeepers of the EU and canon (like Leland Chee, etc.). And according to them (whose sole job it was to dictate canon and establish continuity), books/videogames/comics etc. were C-Canon, and as bekstorm said, were canon as long as they weren't directly contradicted by higher canon. It just gets down to if you, on a personal level, are going to "listen" to the continuity staff at Lucasfilm (who are/were paid by Lucas to establish continuity, mind you), or if you are jus going to listen to George and believe that nothing in the EU was canon. But at that point it all gets very silly, because of 2 reasons. 1.) it's all a fictional universe, and 2.) the books/comics/video games EXIST! So by saying, "oh, all that stuff in that one book you read didn't REALLY happen...", it doesn't really carry too much weight. You read the story, and it was entertaining (or not), and that's all that really matters.
But the fact of the matter is, despite anyone's personal convictions over what "really" happened in the SW universe, according to the official channels at the time, the books DID "happen" and were deemed canon, unless otherwise contradicted by higher sources of canon. But like I said, personally, anyone can choose to invest in the EU (or heck, the movies) as much or little as they want. You see that with the OT purists all the time. And that's all cool, and all. To them, 1-3 "never happened", even though I think all of us here agree that, according to the official canon, they did.