I think that AI attacks those that seem to present great(est) thread, and those that seem to be the weakest. If you have strong armies, or even strong province defense, on all/most of your border provinces your AI enemies will not attack you until they have no other choice left. If you happen to lead in the income/gems etc., all AIs consider ifit is worth attacking you. However, AIs will not attack humans any more than they would attack each other if the situation is similar.
About "cheating AI": AI's of harder difficulties get more gold, resources, gems and resesarch than humans, and all difficulties also get to know who owns what province. They need scouts to see magic sites/armies/lone rainbow-pretenders, and I don't think it's as bad as it seems. Any human player who would consider attacking you would have many scouts in your direction, and he would have traded for lots more information about you than mere provinces!
