Earlier quoted context omitted.
If 20% of your network goes down and you can still serve clients normally, it means that you have a big reserve of machines useful only in case in big outages. I don't know if you can justify it economically. Just spin more EC2 instances ?
Yes, if you use an elastic cloud, by all means, spin more instances :-) Most existing companies still have real servers however.
Most existing companies don't run P2P voice chat networks, either. Using EC2 or some other elastic cloud for emergency supernodes makes a lot of sense, since they can outsource the risk of those machines sitting idle to Amazon.