Honestly, that is no excuse. Even if every black-hat hacker in the world had it out for a certain game, people who buy physical copies of the game should still be able to play it that day.
Botnets aren't particularly expensive to rent any more; you'd have to be pretty committed to taking ubisoft down but I reckon it's doable.
Even if Ubi takes DDoS into account, the DDoS might slow the servers down just enough to keep kicking people out of their games.