Interesting points about real-life tanks. ..For gameplay purposes, having vision in the turret seems to be the only practical way to do it in OpenXCom. After all, if the turret turns to face backwards, you need to be able to see backwards to shoot at anything that's there. ..Plus you get options for strafing, if enabled.
I think tank-vision only confuses people who select the "alternative movement methods" option, without fully understanding it; or who have forgotten about it by the time they encounter its effects. ..I'm not sure there's much, from a game-design perspective, that could be done to make it more obvious, unless the sight-cone was shown visually - but that seems an in-elegant solution.