Comma usage drifts over time. Comma cutbacks were in effect by Dickens time, but his usage would be deemed liberal by today's standards. It seems to me that even in the span of my reading lifetime (five decades), comma usage has become even more sparing.
Something bothers me about this development that I've never nailed down, like a movement flickering at the edge of vision. Today, while reading Nevada Barr's Borderline, I finally caught hold of what it was: the more sparingly one uses commas, the more one is left at the mercy of line breaks.
Commas, or at least the ones most likely to be judged optional, indicate pause. The game becomes "will you see the natural pause implicitly, or must I point it out to you?". As more and more optional commas are left out, what's been subliminally annoying me is that the subtle physical eye movement pause that line breaks impose become more likely to arrive at the most perfectly wrong moment.
Consider Barr's sentence that finally woke me up:
Maybe she was blackmailing
him for money even he couldn't afford or marriage
and a place in society.
I don't know where that line will break on your screen as you read this, but in the book, it unfortunately broke right after "marriage". This had the unpleasant effect of emphasizing "afford or marriage", a syntactically valid construct that is semantically nonsensical. As a result, I had to back up and re-read the entire sentence to make sense of it. In this sentence, it would have been perfectly grammatical to have placed a comma after "afford", and that pause would have made it crystal clear that "or marriage" was only the beginning of the alternative.
In this particular sentence, one could argue that the missing comma is an error because it's needed to show whether the "or" or the "and" binds more tightly. I claim, however, that I could read the sentence without any hiccup if the line break had not landed exactly in the place a pause made syntactic (but not semantic) sense. In any case, this was just the example that woke the camel up -- I'm certain I've seen other situations with little to favor the missing comma apart from how its absence interacted with an unfortunate line break.
The dastardly thing about this is that authors generally have no defense against this. Final fine-tuning of linebreaks is an activity that logically takes place last, after all other corrections are in. In theory, apart from hyphenation gaffes, fixing up line breaks (and widows and orphans, at the page level) should not introduce errors. And, of course, this isn't really an "error", it's an irritant. But even if recognized as an irritant, it would be fairly hard to check for, by either human or machine means.
This seems to me to put a weak bound on the trend towards fewer commas. The odds of this irritant go up the more optional commas you omit, and unless there's no typesetter in your book's future (unlikely unless it's a fairly amateur production), you'll probably have no means to catch such things. On the bright side, possibly I'm the only person who notices such things!
