Yep, wasn't al Qaeda originally supposedly angry at us for having troops in Saudi Arabia? We don't hear too much about that one any more, do we? This is just like Zarqawi beheading Nick Berg, and then checking the newspapers for that week's headlines for something to blame it on. That week it happened to be Abu Ghraib.
I think they're still trying to get back at us for the Barbary Pirate incident. Maybe they don't even remember why they want to attack us. Just that it's the thing to do.