How much of the book spacing is to save physical space? A fair number of larger / more expensive books that I have on hand, and nearly all non-fiction (especially technical) ones, do have additional space between paragraphs.
Potentially all the paperback novels I have within reach do not, though, agreed. They also have far smaller margins, tighter spaces between lines, and thinner paper.
Not sure that matters. My point was that it was a frugal markup. You don't do two spaces because you want more space, per se. You do it to signal a period at the end of a sentence.
Similarly, we don't ever start a paragraph with spaces. Very common to indent opening paragraphs, though. Why don't we space at the first sentence? Because we already have a clear marker for that.
To that end Word is correct to flag two spaces. In all views. Because it is a wysiwyg. You are not writing a markup, you are seeing the rendered target.
They are using markup where they shouldn't be. If, in word, I type italic text using stars, that just means I'm wrong in that context. Similarly, if I use escapes, such that I expect \n to add a new line, I'm just wrong. That doesn't make it less useful where it originated.
Edit: I amusingly had to try twice to get the italic text there. Double stars did not bold. I don't know how to escape the stars.
I would wager most folks that use word have never been the two space crowd. Especially not people that learn on word.
Just like most people that write on paper don't leave extra space after a sentence. We do indent paragraphs commonly. At least, if you are writing somewhere you want it indented, it is incumbent on you to do so. :)
Potentially all the paperback novels I have within reach do not, though, agreed. They also have far smaller margins, tighter spaces between lines, and thinner paper.