Much like some people tune out the speaker and just read the bullet points, I have known people who read just the headings or just the first sentence of paragraphs and then take action based on what they perceived of the document.

There is an argument still, of course, that the PowerPoint situation is worse because (if presented badly) the reading competes with the listening. I would still be hesitant to judge a medium based on bad execution, no matter how widespread. I'm willing to admit that might be unpragmatic of me.