The other thing to think about is how easy it would have been to avoid being taken down in this attack. First do not use DNS within a service. Some companies blamed other providers but in fact it was their fault for using names instead of IPs in a fixed architecture. Second, if a company is stupid enough to rely on DNS, do not rely on one DNS provider. Third, if a company did rely on DNS and had a backup DNS provider, do not wait 2 hours to switch over to the backup.
Now that this attack is history those providers that learned something for it will be easily able to thwart the next one.