Russ, it may not matter to you, for the reasons you state, but I assure you it matters to some. I have definitely lost sales because a cap did not post. Of course I have also lost sales because a pen was too large, too heavy, too small a grip section etc. Whether I want to make a decent postable cap is my business.
(I know that's not what you were trying to say.) What I mean is, that sellability is simply one aspect of this. A crappy-posting cap is just that... crap... an El Grande cap that has an unsightly gap when posted and comes off when you look at it wrong is no asset to a pen! I have sold many a pen with that cap though... that does not make it any better in my eyes!
Having a cap that posts is one aspect of a pen, but not the only one. I view it as a good goal for those that pursue it actively. And if someone wants t omake a postable cap, they might as well do it right!
I do agree only partially with the thread comment. I assume you mean multi-start threads vs single start. It does not matter whether a pen closes in 3/4 of a turn or several complete turns as long as the thread works right and engages w/o fiddling around. What does matter is the holding power of a thread... 4-lead threads typically get so steep they don't wedge in place and a pen can easily come separated, especailly loose-tolerance metal or metal/plastic threads. The current crop of large pens from CSU and PSI all fall into that category. It's the sort of hidden feature that few people think of when they pick up a pen. And if it only sits on a desk may never notice. As far as I'm concerned a single start thread that works smoothly and stays closed is much preferred. I think thread tolerances play a large part, and these guys seem to all design the threads too loose...