Scripted vs AI

Is the ability of Game Developers to use Scripted NPCs interfering with the advancement of thinking AI? Take for example Rainbow Six: Vegas. There are several sections when terrorists burst through the skylight on rappel ropes. This is scripted. It will no doubt cost much more time to tell the enemies to think to come down rather than a point-initiation. This is fantastic- once. With it being a very entertaining game, multiple playthroughs are very predictable, and thus, less fun. Mixing AI into the mix causes some small variations, but it isn't enough to notice something different. So the question is: Is the time/cost of game production causing developers to use scripting rather than inventing or using better AI in single-player games? Is multi-player gaming just an more simple extension of fulfilling this want of varying gameplay? just a thought.