Partly it is because the AI can see the whole map (fow does not apply to him). These are good examples nevertheless. For me its the map that makes the strategic game better and gives an edge to the AI. You can make feign attacks/invasions (taking advantage of the need to cover a wide front with limited units), strategic encirclements, and multifront attacks that trap/eliminate enemy stacks if they are not cautious. You can't do that in the new tw maps though - the stack that loses randomly retreats somewhere in the map.