I think you summed it up quite well, Mike, but I'm not the one who said it. HCB said it and Colin Westerbrook commented on it in Bystander. And, yes, I've used that quote by HCB many times. You can find the same quotes in his book, The Mind's Eye, which, as I pointed out in my annotated bibliography is very small, very short, and very inexpensive. It's one of my all-time favorites.
But none of this really matters. Who cares what "the decisive moment" means or what the exact translation of "a la sauvette" is? I guess Isaac does, come to think of it, but I don't. The important thing is to understand the action that Henri's describing:
"Sometimes it happens that you stall, delay, wait for something to happen. Sometimes you have the feeling that here are all the makings of a picture – except for just one thing that seems to be missing. But what one thing? Perhaps someone suddenly walks into your range of view. You follow his progress through the viewfinder. You wait and wait, and then finally you press the button – and you depart with the feeling (though you don’t know why) that you’ve really got something."
You can't really understand street photography unless you've done it for a while. I know that Stamper, Seamus, and Peter understand it because I've seen their work. All three of them understand what street photography is because they demonstrate over and over again that they can do it. To people who haven't done it, it's an abstraction, and I'll go way out on another limb and say that they don't really understand it. It's like flying. You can have all sorts of theories about it but unless you've done it you have no idea what it's like.