node operators can implement their own throttling - sure - but how many bitcoin node operators are doing that to deflect a p2p ddos attack? even if some are, most aren't - and finality in the network could potentially suffer as a result of a massively scaled botnet attack.

edit: interesting child comment here. not pushing a patch just leaves the bulk of the network vulnerable to being ddos'd by a botnet - potentially resulting in severely lagged finality at best. ip throttling can/should be implemented by being baked into bitcoind.