Both martial arts are about committed attacks. If you are not engaging, there is no energy for the throws. Being hard to throw is easy, being hard to throw while throwing someone else is very hard.
Don, I don't agree that nage's effectiveness should depend on uke's performance. I realize that the committed attack paradigm is the party line in aikido right now but it never seemed like a good idea to me. Why wait for a specific quality of movement when you need to take initiative and end the conflict? Wouldn't it be better if we trained to be effective whether the opponent committed, resisted, feinted or tried to run away? In practical application not everyone gives you a nice attack you can work with.