Are you left-handed. On both mobile and desktop browsers I scroll on the right and the buttons are on the left; I'm right handed which probably makes a difference.
I could understand that you would up- instead of down-vote but surely if you choose the vertical area in which the vote buttons are to scroll then you'd be forever clicking the buttons by accident. I suspect most scroll actions begin either on a scroll bar or on the text of a comment - would be an interesting heatmap to see though.
I am right handed, but my thumb's length is close to the width of my phone's screen, so, when I'm scrolling, my thumb is closer to the left than the right. On the desktop I use the scroll wheel exclusively.
I could understand that you would up- instead of down-vote but surely if you choose the vertical area in which the vote buttons are to scroll then you'd be forever clicking the buttons by accident. I suspect most scroll actions begin either on a scroll bar or on the text of a comment - would be an interesting heatmap to see though.