Is thrusting with a quarterstaff still considered as bludgeoning damage under all circumstances? (From a simulationist standpoint, thrusting with a stave is not an unheard-of maneuver, and can be quite damaging to a target).
Note: I'm more wondering if D&D missed a damage type (i.e. something for being poked with a blunt object, vs being whacked with said blunt object), by the way.
Generally speaking, the damage type of a weapon is to do with how the shape of the weapon influences distribution of imparted force, rather than how you wield the weapon. 'Slashing' weapons have sharp edges, pointy weapons such as spears do 'piercing' damage, and staves, being blunt, are bludgeoning weapons.
That said, I'm guessing you've spotted that particular detail already. What you're asking about is where the line is drawn between one weapon type and another - after all, when you get right down to it, there's not a huge amount of difference between a very blunt spear and a very thin staff, right?
Well, I can't say for sure where that line is, but I do know this: Sling bullets, which are generally much smaller and less blunt than the end of a quarterstaff, do bludgeoning damage on impact. I take it from this that if you want to do piercing damage with a quarterstaff, you'll need to sharpen it into a spear, first - or have some obscure feat or magic that lets you do it, though I'm not aware of such a thing.