I agree with MNIM.
People sometimes get sucked into the 1 for 1 mentality. Each relationship has a different style. As long as the individuality of the relationship is being fed, comparing is a bad game to play.
Great topic, and kudos to you for seeing the differences.
One thing I have found myself doing in any of my poly-style relationships (as a secondary),..is to stop my bf/gf from saying things to me, I know they normally say to their primary. (when I get a feeling, their primary may see it as special.) ...it just seems natural.
I can say, I dont think there is any poor intent. Usually just a slip of the tongue, based on routine habits we all make.