You are right regarding game pieces providing a potential point of reference for maneuvers. The difference is that any advantage from other objects in play is inherent to the game as designed - marked maneuver templates are not.
You are also right that this isn't a big issue, but imagine a tournament game when the last turn ends with your opponent performing a perfect maneuver to achieve the optimal result in one of my example situations while using marked maneuver templates. Maybe he/she would have pulled it off without the help provided by the additional measurement reference, but maybe not. Again, I just don't see the point of arguing against the proliferation of unmarked templates.
Edited by Rapture