Marvel's kind of interestin' in that way... other than Cap and Bucky, few pre-60s characters were so beloved and iconic that if Marvel even THOUGHT about doing anything to them, killing them, changing their costumes, changing their alliances, its BIG NEWS. But look at some of the early and "first" Marvel characters, Human Torch, Namor, the rest of the "Invaders", the other WW2 characters, sure some of them are STILL around and active, buuuuut no one cares that much about them. Maaaybe Namor, but still few outside of Marvel-dom really know of him. He wasn't in the more modern cartoons (that I recall) in such a way that he was instantly iconic and 'sorta known'. So really its a testament to the character that he's endured as long as he has. And I STILL attribute his lasting charm to Stan Lee. He was a wartime hero, he was a 'commie smasher', but I doubt he would have endured as long as he has if he wasn't an Avenger. If he wasn't one of Marvel's "big heroes". And that's Stan Lee's doing.
Wolverine - yes, he was ceated by Len Wein and David Cockrum buuut his REAL popularity didn't come until he was firmly firmly entrenched in the X-Men, which was yep... a Stan Lee creation.
Although I won't deny that certain creators were REALLY what made some of these characters popular. The X-Men were all but canned until Giant Sized X-Men. Spider-Man well... he had a lot of good writers and some not so good ones over the years, but he's still Stan's baby. But guys like Bagely, Romita, McFarlane REALLY put him over the top in terms of iconic status. Think about some of the promo pieces they use for Spidey, those are going on 20-30 years old. Nicieza, Busiek, and so many other writers have kept him 'fresh' over the years. Iron Man is kind of the odd one of the bunch, he's so iconic, yet no one artist or writer over his long history is his "iconic" writer/artist. Sure Layton, Romita, Chen and now Granov have left their indelible mark on the character, but I guess the funny thing is, when they want to show Iron Man, they show either his second Kirby designed armor OR the 90s era Modular armor which the cartoon was based on. Hulk... well Peter David left his mark on the Not so jolly green giant. But I think in the general public's mind, the iconic honor belongs to Bill Bixby.
Cap's a special character because he works so interchangably with the ENTIRE Marvel Universe. You can see him just about every 'universe' and he works. Although I'm still not entirely sure that the whole "Every non-natural born super powered being was because they were part of things that were spun out of the Super Soldier program" hell they even shoehorned Weapon X into the Captain America legacy.
BUT that just goes to show that Captain America is THE icon of Marvel and really that's impressive. Out of ALL the heroes in the Marvel stable, Cap is like the 'god of liberty'.