Yes they all work without that, the example shows how you “can” use all of the plugin stuff, but you can really do it many different ways.
Gripping can be handled on the actual objects themselves even instead of in the character (or a hybrid, the door handle initiates another grip when the handle is engauged for example), and you could run physical hands that directly constraint instead of like the grasping hands which attach to the gripped object and follow it.
The grasping hands attach to follow instead of the other way around as it lets them be used with every grip type the plugin supports. In a stand alone game that, say, chose to only use attachment or physics grips and no others, they may want to handle things differently.