No, it really isn't. There was a five book long Young Bond series last decade, detailing James Bond's adventures as a teen in the 1930's. Around the same time, there was a trilogy depicting the adventures of Ms. Moneypenny, M's secretary, which took place around established Bond novels and gave the character a first name for the first time since her introduction in 1953. Going back to 1973, you had the novel James Bond: The Authorised Biography of 007, which was portrayed as the biography of the "real" James Bond upon whom Fleming based his novels. In 1968, you had 003½: The Adventures of James Bond Junior, which was about James Bond's nephew (who was inexplicably named like he was James Bond's son) which was a Hardy Boys-type thing which flew in the face of established cannon which had explicitly labeled 007 as an orphaned only child. Most recently as the aforementioned Carte Blanche, which could reasonably be labelled "Ultimate James Bond" which re-imagined the character as 1979-born veteran of the ongoing War in Afghanistan (as opposed to a WWII veteran Cold War spy) in a fresh continuity, meaning no prior adventures. Its quite good, by the way, if you like the genre.See what happened there was different. The original works are still (mostly) that, original. They haven't been revisited with alternative viewpoints or prequels or whatever. No one wrote a book detailing the adventures of M in Live and Let Die, or....something about Star Trek (I have no idea there). Instead, the continuities soldiered on with new stories set within the same universe.
Star Trek has had, between all of its various novels and comics and filmed stuff, more prequels and side stories than you can shake a stick at. There are novels detailing Picard's time as captain of the Stargazer, novels detailing Capt. John Harriman (who was in Star Trek Generations for about five minutes) having adventures, novels that detail Worf's time at Starfleet Academy, at least one novel doing the same for Captain Kirk, a short lived comic book detailing Spock's adventures as a member of Captain Pike's crew, etc, etc.
And these are new stories set in the same continuity. A prequel is a new story. I happen to agree that, while Moore did a perfect job giving you everything you needed to know about the characters, there is wiggle room in the original story for adventures we didn't see because we didn't see many adventures from the old days. I'm not saying they'll be wonderful, but I don't find the idea inherently disrespectful or crass.