Good to know about intuitive shots! Didnt knew about the change.
pretty sure headshot has instant travel time and infinite accuracy
Exactly. Yet, my heashots still missing. Should i report as a bug?
The reason why not use physical is in case you have came upon a bow that gives imba increased damage for a certain type, like the one that give +40% blight damage. On my last game as an archer, i got that bow and a t4 arrow with blight damage. Later, i got those t5 arrows with 60 base damage. Than i though they would do more damage with piercing. I did the tests, and the t4 arrows + blight blow was doing pretty much the same "on-hit" damage that the t5 arrow with another bows with piercing and venomous tests. The difference was on the dot + debuffs from venomous later; every fight that should be over before poison or bleed can tick will be over with or without poison or piercing, except when they dont (i.e. bosses), than the venomous proved to be slight superior, not specifically because damage, but because the debuffs, crippling poison specially can give a 40% of talent failure and thats pretty handy against strong enemies.
As for the Steady shot, you are probably right.
The headshot arrow does seem to have a travel time. So it can miss the same way normal arrows do when you, say, shoot a snake and it moves out of the way before your arrows even have a chance to roll accuracy vs defense. Not only it doesn't consume the mark in this case, you will also notice there's no "X's Headshot misses Aerynn the copperhead snake" in the combat log.
IIRC I've seen my own headshot projectiles, and that's with a bow, so one should also be able to see them with enough weapon speed/slowed projectiles.