The key thing to understand is that Marvel is CHEAP thrifty and they would rather give opportunities to obviously talented but underused directors and actors than spend a fortune on someone that everyone knows is good.
Plus they have a pre-existing relationship with Joss on Runaways and Astonishing X-Men.
A lot of what Marvel is doing is convincing people to do their films for less (and signing them to multiple film deals) because being in a "cool" comic-book movie that makes a ton of dough will help their careers.
I like Daphne. I liked her on Friday Night Lights last season and I like her on Heroes with superspeed. That poor kid: She's predestined to either fall for Matt Parkman, die horribly, and/or both. Unfair.