When Phage enters the battlefield, if you didnt cast it from your hand, you lose the game
In Commander, there are plenty of ways to generate unbelievable amounts of energy get something like a Sphinx of the Revelation going and Galvanic Discharge practically removes any creature by the late game
Rather, a second "reflexive" ability triggers when you exile a card this way
Vexing Arcanix was also not really about milling, but anyone who's every played Ice Age sealed knows how often you use it to mill out people in Limited games (if they don't die to the damage first that is)
Gray Merchant of Asphodel has been one of the most valuable cards in mono-black Modern decks for a very long time, and it will do just as fine in the current Standard season
Chapter III allows you to destroy all Walls, effectively dealing with the Artifacts you chose in chapter I for good