Is there a margin of error with a vote like this? Isn't it a direct count of people who want their opinion known? It isn't sampling and trying to figure out what everyone wants.
A vote is an exact count of the will of the people at a given time. There is no error. People can change their minds, but that isn't what the vote represent. That is, a vote is what people who chose to vote said they wanted, not a probabilist representation of what the people as a whole want.