Roger does suggest the vote at the beginning of the novel, and perhaps the best explanation for this is that he is still operating under the constructs of civilization. The boys have not been on the island that long, so Roger has not lost all of his inhibitions yet. He is, undoubtedly, the most evil character on the island, but his suggestion of having the vote suggests that even Roger with all of his evil potential still feels the effects of civilization, law and order.
The lingering effects of civilization on Roger is depicted really well in the scene in chapter four when Roger throws the stones at Henry, one of the smaller children. Roger throws the stones just to the side of Henry, never hitting him, because Roger still feels the convictions of his former life:
"Here, invisible yet strong was the taboo of the old life. Round the squatting child was the protection of parents and school and policemen and the law. Roger's arm was conditioned by a civilization that knew nothing of him and was in ruins" (62).