"the attackers managed to take down a pair of failsafes"
So it wasn't just a DDoS attack, it was a planned attack. Whoever did it had to have scouted out their network to find the failsafes and did so without being detected.
Or is it that a DDoS is just so big that the failsafes where overwhelmed ? Because in that case, they weren't so failsafe.
Either way, Sucuri does not come out of this looking good.