As for Uke ready to jump... Ill tell you, if I know what someone is going to do Im not going to procrastinate... some of these guys know what they are doing and I dont feel like having my wrist out of sorts for a couple of weeks like when I first began. [so they may not be moving for the reason you think. i.e., to make it look like it works, but because it does and quite frankly they are trying to protect their joints.]
When I'm uke I try not to make it too easy for nage to throw me. That being said, there are some sempai who can do a technique so well that I just have
to be ready to fall/tap out/or yell. Or all three.