TWC gets a lot of email, most of which is HTML. However, I still get several emails a day in plain text. Often they've been forwarded a few times and as a rule, the text is splattered across the page, the pictures are stripped out, the formatting has gone dyslexic, and whatever meaning or beauty the page held is gone.
Hot tip: Most people are not going to individually open sixteen formerly-embedded pictures and try to fit them with the now-unformatted text that makes no sense. It's mind numbing to do so and the delete key looms large.
Worse. Try tracking a conversation back and forth in plain text with all those > > >. After two or three replies you've lost the rabbit. I'll try to keep up if it's a friend or a client, but I'm grumbling the entire time. Eventually, plain text requires that you excise the relevant parts and paste them into a new email just to beat back the urge to inhale fumes from the tailpipe of an idling UPS truck and slip gently into that good night.
In the heyday of plain text, emails were terse and direct, with little flourish or flair. Plain text was all there was and, like a loin cloth, it served it's purpose. In modern America, we are half past 2008 and plain text email is a relic, a dinosaur, the Neanderthal of the modern computer world.