The arrows do not count as projectiles. They are merely a visual effect. https://wiki.guildwars2.com/wiki/Barrage
***A projectile is a ranged attack which must travel from the user to the target before dealing damage.
Most projectiles can be avoided by dodging, blocking or reflecting. Projectiles can also be obstructed by environment, or by other enemies in their way, though this can be negated by piercing. A few projectiles auto-track the target as it moves. Projectiles will travel further if they are fired from a height. https://wiki.guildwars2.com/wiki/Projectile***
Why is that? I'm so tired of being in a structure and having a Ranger/s outside of the structure with ZERO line of sight, but still able to fire through walls, gates, etc. to destroy siege and down/kill players inside! Shouldn't a Ranger's arrows be a projectile that is blocked by structure's/environment? If Barrage is working the way you intend it to, let me know Anet. I will move on.