Basically what you are saying is that uke is wired to fail from the beginning, not as a result of successfully completing the equation of the kata, but because they don't hit you, they are not a threat in any way.
If that's what you think I said then I clearly didn't express myself well. I'm saying, in an environment where nearly everything is defined (who attacks, who defends, what the attack is, what the target of the attack will be, what the response to the attack will be) is a kata environment (which may not be the best word to use.....) I submit that such an environment is not the place to worry about timing. If you know that I'm going to strike shomen to the top of your head, it's very, very easy for you not to get hit by a shomen strike on the top of your head, regardless of our respective skill levels. This training environment, as Ron noted earlier, is a set up. It ain't real. I'm convinced it's a waste of time to try and make it real by taking about "what if?". What this environment (kata) is ideal for is instruction. It's perfect for that. It may even be vital for instruction. So let's work cooperatively there for however long it takes (probably 5 - 15 mintues).
After that, let's take this technique that we've been instructed on and put it in a dynamic environment or a drill or a scenario and work on timing there (the majority of the class). Here we can create an environment where it's ok not to succeed, where people can play and see what works for them. In this dynamic environment it's ok to reverse your partner, it's ok to change to a different technique, it's ok to get thwared and all those other things that happen and cause the "is this person a jerk because when we train they...." posts that appear here on a regular basis.
In short, I believe that:
Alive, functional, and motivated uke
cannot exist in an environment where they are: 1. "uke" 2. have a specific attack 3. with a specific target .... because those things define a kata, and kata ain't dynamic.