Yes, and I remembered the comment when I was reading it.
However, like with every piece of advice in this thread, someone else says the opposite, and I seem to recall someone posting a couple of weeks ago saying that no matter what, bloodrazor will always do less damage than more AD/crit/AS/whatever, because the %HP magic damage bloodrazor does can be reduced by magic resistance. Something like that. And it's not like warwick will ever have AP or magic penetration.
I didn't see your Annie, but I'm going to guess they were either A) new or B) trying to use a mejai's and failing miserably or C) both.