I agree with you, in that you're saying it's silly for RockYou to assume their customer's passwords are unique to their service, but I vehemently disagree with

I agree with you, in that you're saying it's silly for RockYou to assume their customer's passwords are unique to their service, but I vehemently disagree with your unstated assumption--that 99.99% of other communities aren't just as likely to have users pick dumb passwords. I don't mean this to come off as ad hominem, because I don't think it was your intention to leave the opposite side of the argument open and I think you personally understand the issue. I just think that we shouldn't have a mentality of "aww, we need to take special care of these unsavvy users." Not having basic levels of security in place for any user-base is simply unacceptable.