In late autumn of 1985 (if memory serves) I was sitting with my friends in a classroom at my high school (the High School of Art and Design in New York City) awaiting a guest speaker for our Comic Book Club meeting. Each club needed a teacher to sit in on the meetings and we were lucky enough to have one with connections in the comic book industry.
I don't recall the guest's name but I remember he was a writer and sometimes editor with a number of years in the business. His speech that day was about the process by which a concept goes from pitch to final product. It was very interesting, at least for me and I learned a lot about how business and creative ideas can often clash and just as often find a way to work. By way of example, he told us about a new project DC was working on. He couldn't say too much but seemed very excited. He thought it was going to be the 'Next Big Thing'TM. It was called Watchmen.
Our guest described the series as a gritty and dark look at what the world would be like if superheroes really existed. How the world might be better or much, much worse for them being in it. When asked what superheroes would be featured he said, "They're using the Charlton Comics heroes. Blue Beetle, The Question, Captain Atom...those guys."
This excited me in the extreme. I was a huge fan of those characters, having received a bunch of Charlton Comics from my uncle. Also, we (my friends and I) all knew DC had acquired the Charlton characters since they had appeared in Crisis on Infinite Earths.
Fast forward to 1986 and the release of the first issue of the Watchmen limited series. I was initially disappointed to find original characters in it and not the ones I was expecting. These were not my Charlton heroes but dopplegangers made to look like them.
Then I read it and as I continued to follow the series I found it gripping, moving, very depressing and way cool. It quickly became and still is one of the greatest achievements of the sequential art form and definitely a personal favorite. I am also really happy they didn't use the Charlton characters. As I don't want to spoil the film or the graphic novel for anyone who still hasn't read it (there must be somebody) I'll just say that it would have made it impossible to use the characters in any other project. Blue Beetle and his friend should be fighting side by side with Batman and Superman. The Watchmen characters belong to the Watchmen world.
A final thought...
I read a Watchmen Wiki that said writer Alan Moore didn't base the female character of Silk Spectre on any existing Charlton character as he did the others. Instead, it says her design was inspired by DC characters like Black Canary and Phantom Lady. Perhaps so, but if they had kept with the idea of using the Charlton heroes, does that mean they wouldn't have used Nightshade?