That doesn't really address the XKCD. The XKCD was comparing schemes where the attacker has perfect information about the password scheme each user is using. Pa

That doesn't really address the XKCD. The XKCD was comparing schemes where the attacker has perfect information about the password scheme each user is using. Password crackers therefore cannot be "on to this trick" as it is assumed they already know in the initial calculations of entropy. Given that Bruce Schneier is Bruce Schneier, it seems likely that I am wrong somehow, but at present I cannot see in what way.