What makes Vault Hunters so different from everyone else?

Solution 1:

Aside from the Sirens who obviously have special powers, not that much. "Vault Hunters" is just a term used in-universe to describe treasure hunters and explorers. Vault Hunters are the people who haven't died yet; as some NPC in Sanctuary puts it, "Are you the hero, or are you just the best at killing people?"

Gameplay-wise, you're actually not all that much different from NPC characters other except your skill and ability to revive. If you actually take sustained fire you will die pretty quickly. You have your skills and stuff, but compared to Skags that spit lightening and Goliaths who's skulls pop out, characters that can (badly) clone themselves, stalkers who turn invisible...you're really not that special, you're just not dead yet, and you've got some friends in high places (like Claptrap).

Solution 2:

Well, I don't have much evidence to back any of this up, but here are my thoughts:

Running down your list, in a way you answer your own question: none of the Vault Hunters are exactly normal people. Brick and Salvador are physical deviants with far more muscle than the average person. Lilith and Maya are Sirens. Roland and Axton have military training and equipment. Mordecai has mad skills as well as a violent pet. Zer0 is some kind of freak- possibly a robot- and is a master assassin. Gaige is a prodigy, and Krieg is an escaped experiment with (presumably) super-strength. So you could say that each of them brings something to the table that normal people don't have.

Second, for a lot of them, the fact that they decided to pursue a career as a Vault Hunter was spurred by the fact that they were made for it- or weren't made for anything else. Going by ECHO recordings found in BL2, both Axton and Zer0 chose Vault Huntery because their respective jobs (hitman and assassin) weren't challenging enough. So it's not that being a Vault Hunter makes you strong, it's that choosing to become a Vault Hunter and going through with it means that you're probably have what it takes to make a good one.