Problem that has nonlinear impact on performance can not be solved by adding of two more servers...
Simplest example is index in database. Before adding of index it takes 2 days to execute it, after adding of an index query executes in 100 milliseconds. How can you solve that by adding of more hardware? Also you usually can not solve IO issues between app and DB servers by "just adding of two more servers"...
Not to mention that when it comes to scaling of DB you really can not just depend on "adding of another server in cluster"...

Actually it is interesting approach... If you cant force ISP of an foreign country to comply by law, you can just nuke them with yet another botnet so bad, that they will be forced to buy a equipment, resources and do the legal work with their peers to be able to maintain QoS in case of DDoS... So when next time somebody uses their networks to stage DDoS, they will be ready and able to track the stream and filter out zombies...