I'm not sure Nathans theory is correct but...

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.

The point is, to prove a point a DDoS attack can be initiated against Ubi's authentication servers thus making the game unplayable for extended periods of time for legitimate customers only.

Even if Ubi takes DDoS into account, the DDoS might slow the servers down just enough to keep kicking people out of their games.

Agreed, on initial release the DRM server would be getting hit major amounts due to the massive amounts of pre-orders. You don't pre-order unless you're planning to play it in that first week it's on sale.

And we all knew that with the publicity surrounding the new DRM, something like a DDoS at release shouldn't have been a surprise. Ubisoft really should be prepared for these attacks.