The latter is possible in nearly all games. But that isn't necessarily a direct function of gameplay.
For example, I can not "jump" out of the way of a fireball in Everquest. Having jump as an action has no function outside of traversal. Which has no gameplay function, only interaction with the environment. We could consider interaction at a high level a type of gameplay- though more gradually we would call these game mechanics.
However, in GW2 I can jump out of the way of a fireball. That is gameplay in both the over sense of general mechanics and operation of play- and in the granular sense of game mechanics as in the exact operation and mechanics of play.
GW1 is kinda more like EQ. Jumping really would not have mattered much to the gameplay. There were no mechanics that needed or allowed traversal to effect the instance of play other than to say getting from A->B.
So why do you need to jump in GW1? [rhetorical]
Now if one were to say, "I think jumping in GW1 could have been used to enhance or add to blahblah mechanics." Sure, that's a potentially interesting speculation.
It is only in the sequel that Anet used the jump action as an actual element of game mechanics.