From my experiences the the same rules apply to the ai as well. I had a war initiated by my neigbors, the netherlands. They declared war. Everyone was in demo. I bought several other to join on my side, namely first the russians, our common neighbor. The netherlands never switched from democracy, even when losing city after city. I assume every war declaration gave them the -30 points, witch outweightes the points for losing cities and units. The russians on the other side switched quite fast to faschism. They declared war and suffered heavy causalitities from the beginning. So i would assume war weariness does count for the ai, at least certain aspects.