That does fit my personal experience, which has been that when comparing old-school open-source communities where people know how to do proper quoting on mailing lists vs. internal e-mail communication at an Outlook-centric company that does a lot of remote work by virtue of being geographically spread over the world, the quality of technical discussion is much higher in the open-source communities. A large part of that is indeed that sub-points and/or nuance of earlier e-mails is simply dropped on the floor in the Outlook culture.

I suspect that it's not just about taking time to inline quotes, but also simply about seeing what you're replying to directly next to your answer, as opposed to having it be separated by at least a large message header and likely by much more.

Another sad fact is that people re-invent inline quoting in Outlook culture all the time, badly: they manually copy relevant parts into their top-posted response, or they use some sort of color coding to write their own response inline.