I think it's fine to still call it that descriptively; I don't agree that an official rename means we "should" do whatever the corporate branders desire. It still is the Penny Arcade Expo in the sense that it is an Expo, and it is owned/operated by Penny Arcade. It's true that the Penny Arcade corporate marketing team has officially redefined the initials as not standing for anything, but that's only really binding on their own marketing materials, not on everyone else.

My guess is that they think you were implying it is a different expo. Not just in name, but in content and such, as well.