Again, it doesn't protect you, it just buys you time, because the attacker has to start that far back in the chain and build a longer chain. But the attacker will succeed (given enough time).
But in my attack, the attacker doesn't have to start "far back" in the chain. He starts forking it from the last known legitimate block... (sorry for my multiple edits, this is complicated)
Well in that case, the attack would have to be ongoing for as much time as the number of confirmations. In the two hour attack, you can go undo 6 confirmations, in a two month attack, you could undo 600 confirmations (or whatever). Confirmations is still linked to time somehow.
Please answer to my posting: Your attack still assumes that you can split the internet. That you can dictate what blockchain each miner can see.
All the clients use the longest rule-following blockchain. If you can provide a longer one then the current one, everyone will use it.