I was actually thinking about this a bit recently... are we sure it's even a DDoS and not due to higher traffic? A sudden burst of real traffic could cause issues as well. I learned this first-hand when a major site linked to one of my articles and my ~300 visit/day site got over 35k visitors within an hour, crashing it over and over in the process.
A sudden burst of traffic should not cause issue that easily because mellow ads should have a good server for traffic and even if the cause is really because of the traffic burst then batardo should know it right away as it is not hard to examine if the cause comes from traffic