You're just making the same point I did, except from the standpoint of what the defensive mechanisms are, so I'm pretty much in agreement except for one thing:

Did it ever occur to you that I don't do so simply because I have other things I'd rather talk about, like snook fishing and dinghy camping and alien civilizations and hoplite phalanx battle tactics? But if all my posts were about any one of those topics you and the others would have thrown my butt out a long time ago, and deservedly so.

It would have to be over my dead body. I find detailed and interesting posts about things I don't know much about to be fascinating, and when done by a skilled writer, even more so. You could post about nothing but boats here for weeks, and I'd bet almost all of us would be fine with it. If Mary Anne, for example, talked about nothing but her library work, it would still be worth reading.