I think it's true in any group that a certain few feel like they do everything and a certain group feel like they are never asked.
I like the roll call idea. Im in several community and civic groups and I think that what happens is that you KNOW so and so will get it done or has always done it so that's the path of least resistance.
IMHO, all jobs should move around and nobody should remain the committee person in charge of anything for an extended period of time (no matter how great of a job they do) because it either stagnates the process or burns the person out.