Does the product owner actually vote on the size of the story in Scrum or is it just Dev/QA?
I was wondering, because it does not really seem like having the product owner vote is productive.
In "classic" scrum, the team decides on the estimates and commitments of a story without the PO. The story in the backlog is discussed by the team and the PO and then agreed upon by the team.
EDIT : as nuqqsa and xsAce pointed out, the presence of the PO can be helpful during the estimation session, as he can help clarify the exact requirements and thus make the estimation more precise, but he does not take part in the actual estimating.