I found it awkward at first that they were this way round, partly for the positive-x reason you give, and partly because I'm right-handed so although visually I scan the line left-right I control the pointer with a mouse that sits significantly to the right of my eye-screen line, so when moving the pointer I essentially have to pass over the -- to get to the ++ I made a couple of voting mistakes early on because of not paying sufficient attention to which vote I was selecting.