Sion does not gain AS from items during passive.
Why? :c
Why? :c
Because he gets set to 1.75 AS, independant of items.
FYI, that is WAY more than he should reasonably build.
Probably so that people wouldn't be baited into building damage items on him.
Probably because he gets 10% enemy max hp on hit + his normal damage and a set 1.75AS? Also, because I don't think Riot wanted the best way to play Sion being full AS and then dying.
So people will not build Zephyr on him.