You answered more than I expected. It all makes sense. Now, just some 'observations' ...
(Oh, yes Henry, I got it all. :) )
I didn't think the shakes came in that much 'contact' with the housewrap since the shakes over-lap each other (which leads to essentially 1 edge of a shake coming in contact with the wrap.) Of course, this is not the case with the starter course. Secondly, I didn't realize the shakes bled that much. Thirdly, I didn't realize that the shakes can 'tighten up' the house so much that vapor can't get out from behind it. (Wood has a tendency to expand, contract, thus 'move', and create openings to let the moisture out.) I mean, how does painted stucco breath? Fourthly, IMO, ANY siding that 'requires/calls-for' tar paper as a barrier should be banned. Geesh, how WILL the house breath??! RE: backpriming, that's interesting.
Now, I have NEVER, EVER hung shakes. (Nor do I want to if I have to 'wrestle' w/my conscience on wondering if I'm over-doing it, or not doing it right.) Althought what you say makes SOME sense (it's just the 'degree' of sense in my head), I've never, ever seen strips hung or back-priming done. I'm now wondering what that says about those pros that hang the shakes. I have seen tar paper installed, and maybe that's their 'only plan'. HOWEVER, I'm a fan of letting the house breath (implying that I like housewrap, and hence would need strips.) Oh, I have to admit that I can't recall if I've seen shakes going up DIRECTLY on a housewrap. As I mentioned, I've NEVER seen strip installed or backpriming done in ANY 'scenario'.
Well, it's all very interesting information, and I will 'refer' to it in the future. I will also 'state' that I've never done an install and can only 'support' the explanation based on experience by others. (This isn't new - Only this 'case' is new.) Thanks again and see ya on the Forum.