Well, the Skull was the one who gave him the name Crossbones, because he intended for him to be his sidekick or whatever. I guess they could introduce Crossbones without the Skull being involved, but that would be sort of strange if Cap keeps running into villains with names that reference bones.
Casting for Marvel's NETFLIX shows:
Daredevil: Ryan Phillippe
Iron Fist: Philip Winchester
Luke Cage: Billy Brown
Jessica Jones: Michelle Monaghan
The Punisher: Holt McCallany