Kennen and Twisted Fate - Elelctrical Surge v Stacked Deck

This is specifically about the passive portion of Kennen's W, Electrical Surge, and Twisted Fate's E, Stacked Deck.

Both passive states that after X auto-attacks, the next auto will deal bonus magic damage. Simple, and because they're both considered on-hit effects, they should work the same way, right?

Wrong.

The differences are so obvious it hurts.

We'll start with Dodge, Block, Parry, and Blind.

Twisted Fate - Bonus damage can be Dodged, Dodging and Blind will cause the stack to not be consumed. Even if the auto-attack is Blocked or Parried, bonus damage will still go through, and the stack IS consumed.

Kennen - Bonus damage CANNOT be Dodged, both Dodging and Blind WILL consume the stack. Block will not mitigate bonus damage, and consumes the stack. Parry negates bonus damage, but still consumes the stack and mark is placed.

Twisted Fate - If the target for his empowered AA is killed before hitting, the stack is not consumed.

Kennen - If the target for his empowered AA is killed before hitting, the stack IS consumed.

Twisted Fate - Twisted Fate can stack against towers, but the empowered AA is not consumed when attacking towers. Spell Shields will block ALL damage.

Kennen - Cannot stack while attacking towers. Spell Shields will NOT interact with Kennen's empowered AA, therefore NOT mitigating any damage.

Seriously, why are two passive abilities that are essentially the SAME on-hit ability with only a different stack counter treated DIFFERENTLY in so many different ways? This is counter-intuitive and forces players that play these champions to remember small, almost arbitrary distinctions that have DRASTIC implications on gameplay.

Effectively speaking, why are the two treated differently?