In the case I ran into a creature hit with a Piercing weapon caused its diseases to splash on the character that hit it.
So a Dagger could use Slashing and be fine but the Morningstar can't choose and causes the splash back. The whole thing grew bigger as the player was using HL and it showed it as P/B weapon and it was not until I showed the core rules that it was AND not OR for a Morningstar that the "discussion" ended.
Funnier was same session the PCs where in water and Bludgeoning/Slashing weapons do Half damage. So again as it was the Morningstar guy wanted to not take the half damage as it was a B/P weapon.
Not saying your not correct about DR but the above are to places where it does matter actually.
Its not a huge deal actually and more of a note that it should correctly show the values but I figured it would end up SUPER low on the priority list.