Allow me to start with an admission: I’m a HUGE Marvel fan. I have a picture of me and Stan Lee on my desk; I went to the Iron Man marathon this summer; I worked on, and have my name is in the credits, for two different Marvel games; and I own every Marvel hero movie released in the last six years on Blu-ray.
So you can imagine how excited I got when I heard they were working on a TV show about S.H.I.E.L.D. However, my excitement was matched by my confusion over how they were going to do a Marvel show without any of the main cast having super powers.
But apparently, Joss Whedon and Marvel anticipated this question from fans, as the preview for the pilot explained it all with one phrase: "not all heroes are super."