Horticultural reasons dictate the way a tree my grow naturally, those reasons my be better be understood as genetic forces as opposed to horticultural. A tree with tendencies toward weeping will have branches that hang down, though in general such trees are too extreme to be useful as bonsai I wished only to demonstrate a point. When we think in terms of horticultural reasons we usually refer to the way trees are treated or cultivated.
In bonsai it is not uncommon for a trees natural tendencies to be ignored for the sake of art. A needle Juniper is by nature a low growing shrub that does no exist naturally in many of the forms it is cultivated as a bonsai. The same can be said of a majority of Junipers cultivated as bonsai.
To the point of your pine question: It is possible to style the branches into forms that are contrary to how the tree my naturally want to grow. It is for this reason that techniques of pinching and pruning become so significant.
I might add at this point that it is a good thing that you not only notice these things, but that you take the time to analyze and sketch these differences, this practice will take you far in bonsai.