Peaceable follow's up on #3: Sugar or Not?

In a previous post, Vivi reflected on the mousse she made at Mother's house without additional sugar proved to be heavier and darker than the mousse made with sugar that she made in OR. I had the same experience--both of us using ghiradelli chocolate chips and sugar obtained a lighter, fluffier mousse than we obtained using gourmet bittersweet chocolate without sugar.

So yesterday, I made another chocolate mousse using up the same gourmet bittersweet chocolate, but this time I added the appropriate amount of sugar. (I also used cointreau rather than whiskey and eliminated the hazelnuts.) In any case, this mousse was much lighter and fluffier in texture. So I'm guessing the sugar is instrumental in texture. Interesting!