These leaders are passionate about their work and this passion evokes an emotional response on the part of their team. The response is not directed towards the leader. But rather it is an emotional response to the goal. The individuals on the team become invested in the successful achievement of the objective and this is a reflection of the passion modeled by the leader. Call it pride of accomplishment; a willingness to go the extra mile; that 'never say die' attitude. Regardless of how you choose to define it, it boils down to a commitment to the goal that is evidenced by a higher level of personal devotion than might otherwise be anticipated.
Think about times when your leader has failed to have a passion towards the team’s objective. How did that impact your commitment? How willing were you to search for the answers or make the effort to overcome a particular challenge when the one most responsible for the outcome chose only to be involved in the efforts.
A passionate leader is a committed leader. The difference between commitment and involvement is best defined by the story about the breakfast of bacon and eggs. In this analogy the chicken is involved. But the pig... the pig is committed.