It's kind of picking nits, but there is, in fact, a difference.
Comic books have been being made into radio plays, TV shows and movies pretty much since the beginning. Superman had some (actually very good) cartoons even back in the 1940s, and the George Reeves TV show in the 50s. Batman of course had the famous campy TV show in the 60s. Wonder Woman had her almost-as-bad TV show in the 70s.
The thing is, in effect nobody took them seriously- Superman was a blockbuster, that rapidly ran itself off a cliff with the sequels. As did Batman- the first one was great, but they just got sillier and stupider after that.
It wasn't until X-Men that both the characters and the audience were taken seriously. The movie was filmed seriously too, by a fan of the original comics, as something other than campy nonsense for kids and tweens.
So I suppose we could say Superman showed they could make a "blockbuster" moviw out of a comic book, X-Men showed they could do it seriously and faithfully to the source material, and Iron Man showed they could turn it into a proper franchise (IE, and not run it into the ground with batnipples and puns. )