That's not fair, of course: Tobey Maguire bulked way the hell up for Spider-Man, and any attempt to wedgie him now would end with the assailants finding out what their own teeth taste like. And Elijah Wood played that creepy dude in Sin City a little too well to be pure acting; you know that guy probably carries around a claw hammer everywhere he goes and just waits for some meathead to scratch his murder-itch.
But even though you know it's objectively silly to sense any kind of nerdly weakness in them, it's still there, isn't it? They each have this vague, victimized-and-now-I'm-totally-unstable-because-of-it aura. The interchangeability is even acknowledged in their own movie roles: In the Spider-Man comics, Eddie Brock -- the man behind Venom - looks like this: