This might be a function of how passively many people read, though – particularly as compared with the highly interactive posture of speech.
There are reading strategies which we can employ to engage the brain quite effectively.
Plus, writing is immediately replayable. Some would rather abuse this than rely on a more holistic reading strategy, but that doesn't discount the value of having a concrete, immediately-accessible, and yet persistent record of the communication.
Having someone tell you something is vastly better than reading it.
Aside from the intonation and stresses in tone there's also a plethora of body language and cues to pick up on.