. . . my current working assumption is that the copy I pasted into the post under discussion may have been composed in one of the problem text editors . . .

Bingo, S!

. . . although that still does not explain why I don't see the odd characters.

I suspect that's because "Note Tab Light", which you're using to compose in, recognizes the special characters. Their weirdness is transparent to you.

Here's something to try: cut and paste a passage from that web site into a plain-vanilla ASCII text program like Notepad. Then re-copy the Notepad version into a post window here - in this thread, for instance, and label it "Test". Post it and see what happens.

I see from the string at the bottom of your posts you're using Win 98 (so am I) and IE 6 (I used to). If you have Word set as your default text editor in IE, you may still have to turn off "curly quotes" in Word to cure the problem - but I'm not certain about that.