I understand what you are saying. I would not dare to suggest to tighten the hold until aite taps...because what if aite does not tap....always with feel and awareness. But I think it is not really important why aite taps out (also see katherine's example), only that you release when he/she does.
Well I disagree here. It is very important to be aware of why uke is tapping out and that's basically my main point. If you're not aware of why then you prohibit your own learning.
As I've said earlier you get ukes tapping out because of what they think is about to happen, usually based on past 'bad' experiences. That's not the time to let go.
Are we teaching people to recognise reality here or are we teaching them to fear?
It all sounds good that you must let go no matter what but on inspection I find it's not always the case.
Now before you think I am mentioning a very rare occurrence I assure you I am not. The number of times I have come across people tapping out for what they assume is about to happen and the number of times I have come across people throwing themselves into perfect, artistic, breakfalls for what they assume is about to happen is numerous.
Fear of what might be causes this including avoidance of possible pain. Aikido in my mind should be teaching how to face, harmonize with, be in present time. Thus I am not led by false tap outs.