There aren't that many characters that have such lengthy pedigrees. I think there are a couple of factors for that. One is the medium. Getting new generations to read a book that you loved in your childhood is much more difficult than getting them to watch a TV show that you're nostalgic about. The medium of our entertainment has changed so drastically in the last 100 years, I have to think that we'll see more and more characters outlasting normal lifespans. And the cycles starting. Properties that were popular in the eighties like GI Joe, Transformers, and Teenage Ninja Mutant Turtles are seeing new life now that the kids that enjoyed them so much twenty-five years ago are parents themselves with money to spend and memories to share.
Another factor that can help a character last through the generations is change. I've talked about this before with the saga of Buck Rogers (http://www.doabarneyoldfield.blogspot.com/2012/09/buck-rogers-man-of-future.html) and how change is difficult for that particular character. I've briefly touched on that with Superman.
The change in Superman has been well and thoroughly documented before. But in case you're unaware, let me explain. During his debut in the 1930's, Superman was very anti-establishment and a hero of the poor and suppressed. In the 1940's Superman fought Nazis and war saboteurs. In the 1950's he was very much an establishment figure and a duly deputized member of law enforcement. The 1960's saw slow change for Superman and he suffered for it, quickly gaining a reputation as a tired old hero of former generations. In the 1970's his popularity surged again with the Superman movie. In the 1980's he and his alter-ego Clark Kent were completely rebooted, all their history jettisoned, and they were re-imagined for a 1980's older teen audience. In the 1990's, Superman died, came back, grew a mullet, changed powers, and did absolutely everything to stay relevant.
The point is that the most enduring characters, especially those backed by money making corporations, are always changing. Superman, Bugs Bunny, Mickey Mouse, Spider-Man, and more.
I read a line recently (I apologize, but I can't find the original material) that suggested the story of Tarzan only works in 1912. The thought is that in today's day and age with how much our jungles have been explored and with our current technology that the story of Tarzan is just not believable.
Come to think of it, I haven't seen many versions of Dracula that cast him in a modern-day environment. There have been plenty of updated retellings of the story, but most of them cast the character in the era in which he was originally imagined. Nevertheless, the character proves to be too popular to fade away.
I remember seeing Roy Rogers old television show for the first time with my father-in-law. There was a jeep! The famous western cowboy was set in the modern day 1950's! This really surprised me, as I thought of all western characters being from the old west era. Seeing Roy ride Trigger next to his sidekick in a jeep was a little unsettling for me.
In the 1940's, there was a series of Sherlock Holmes films starring Basil Rathbone and set in the modern day. The first time I saw Sherlock Holmes fighting to stop Nazi plots, I was a little unsettled. It seemed odd and out of place, but ultimately worked. And it was obviously very natural for the audiences of the time.
Part of the reason Superman sees change so much is that he has seen continuous, unbroken publication every month since his first appearance in 1938. Few characters have this advantage and even fewer mediums offer that kind of opportunity. So to comics fans, change in characters is nothing new.
But could you picture Tarzan with an GPS? Dracula being discovered because his image doesn't appear on an iPhone screen? Sherlock Holmes fighting modern day killers and criminals?
P.S. And yes, I know all those things have happened. That's part of the point.