You know, I am surprised we don't just code into Bitcoin to shut down if faced with a need to reorg more than 5 blocks, rather than accepting an attack chain. Then all an attacker can do is temporarily DoS a chain - far less disruptive than rolling back transactions.
Because for the low price of 250 BTC per event I could knock down bitcoin world wide as often as I want.
How are you going to do that without the majority of hash power?
I would ask the same question alone, and also with the consideration that each "event" motivates development and refinement of clients performing automated analysis on the competing block chains to make a more intelligent choice. (e.g. automated analysis of the transactions in the competing chains, and a bias toward keeping the chain that causes the least disruption instead of an automated shutdown)