In Rick's (and Steve Smith's) own words, from my 2005 copy of RS France, "Destinations covered in this book are balanced to include the most famous cities and intimate villages..." "We've been selective, including only the most exciting sights and romantic villages..." "We cover just the best... The best is, of course, only our opinion. But after more than 35 busy years between us spent travel writing, lecturing, guiding tours, and satisfying our Francophilia, we've developed a sixth sense for what touches the traveler's imagination..." "Since this book is selective, covering only the places we think make the top month of sightseeing..." (my bold, not his)
Adding my own thoughts, I believe the Rick Steves books are best for travelers who are visiting a country for the first time. As some of the other posters have said, and as quoted above, your average traveler, on a first trip to France, and having just two weeks to fill, will not be spending time wisely if they go to Dijon (or fill in the blank with any other city or village not covered in any of his other books). If one is fortunate enough to visit a country more than once, there will probably be a need or desire to supplement RS's book, but one will probably continue to find his book useful for many trips. It's only after 18 years of visiting France nearly every year that I'm beginning to feel that I almost don't need his France book anymore! And, I finally made it to Dijon only during one of my most recent trips.
On the topic of comprehensiveness, I would point out that my 2005 edition of RS France is 654 pages. My 2020 edition, which has a nearly identical Table of Contents, is 1203 pages! Somehow he has nearly doubled the pages, while dropping an entire region (Basque Country). In France, I supplement RS guides with the Michelin green guides (and many other resources). There are over 30 regions, each covered by its own green guide, 400-600 pages in length. For my upcoming trip in the Charentes region, using one of these guides, I'm still finding gaps in coverage. It's just impossible to write a book that covers everything.