10 LRPD Points[tm] to the first person to name the movie.
Very good points, and key I think to understanding why Bryce doesn't understand what we're talking about.
Relational sets have a very different algebra than graphs. Yes, sets are very powerful (and they have their own native means for representing hierarchical relationships, such as nested set trees), but they aren't the entire world. Being able to think in both worlds vastly expands the range of solutions one can provide.