Maybe not, but they often are! Gerrard often bails out Liverpool, whereas a great captain should be demanding the entire team plays well rather than bailing them out all the time. I don't think it's enough to simply set a good example, you have to rally the team and demand they do better, otherwise you may as well let Beckham captain England (and he's not much cop).

A capatain is meant to be the managers representative on the pitch, not a virtuoso, that's what a star player does... And they rarely if ever make good captains!