People were quick to blame GameStop, as is often the case, and while the retailer still shoulders some blame in this (if only for the practice of opening then re-selling games), the game's publisher Square Enix appears willing to fall on a sword and accept a little responsibility, saying it respects Gamestop's "right" to mess with the game.
"As part of Deus Ex: Human Revolution's boxed offering on PC, Square Enix included a third party coupon", says a statement released by the publisher. "GameStop was not made aware of this inclusion and Square Enix respects the right of GameStop to have final say over the contents of products it sells and to adjust them where they see fit in accordance with their policies."
It's funny that GameStop would take such drastic action over a game that, Onlive coupon or not, was still being bought in its stores. What's it going to do next, yank every game that has a mandatory Steam installation?