I've been playing MTW since it came out and have never seen the AI hop across a hostile blockade and attack me. There has to be an explanation for this somewhere.

As far as the AI and money, maybe they are better at budgeting than you are. I generally spend everything I make for a while in order to beef up security right away. It's possible that in your case the AI had a large budget in reserve and was using that to build imporvements.