I also prefer plain text, but I'd rather have useful tools to deal with the needs of the business, while offering plain-text as an option for people who prefer it.
There's ONE THING ONLY that html email is good for. And that's alerting me to a sender's failure to understand the fundamental natures of the different coding schemes for the written word.
Maybe it is just that most people have never been exposed to properly formatted text emails?
I'm sure people find most of the websites they visit and the emails they read, filled with columns of extra garbage, to be cumbersome and difficult to read. Executives think that's what people want, but I doubt there has ever been an thorough examination of all the formats and their effects on people.
Comment nesting must have been awful. Or did you cheat and use pseudo-graphical characters to overcome the obvious limitation of plain-text for such a purpose?
Do you eschew the use of typographical techniques that aid reading, both speed and comprehension, such as emboldening, headings, breaks, italics, font and colour changes?
I never understood this "email should be only plaintext" argument. Getting information across is easier with options for images and textual enhancements. Do you use lynx for web browsing?
When the KMail people were refusing to allow people to use HTML to reply to HTML emails properly one guy argued with me that to send photos to family members I should use FTP, send an address so they could log on and dl the photos to view - that this was somehow better than having the images there ready to view in the MUA.
It is interesting to note that some of the most important works produced by mankind can be reproduced in essence without these aids [1]. Moreover, these well-meant aids are perceived as undue distractions and hence disabled by many [2], most of which are not die-hard plain-text users.
Gutenburgs top projects are Kama Sutra, Sherlock Holmes and Punch - whilst Burton's original translation was text only I think you'd be hard pressed to argue that the first of these has no need of illustration. The second is a [series of] novels, plaintext is fine there though often even novels have images ("plates") of some kind. The third, Punch is probably best known for it's illustrations and it's conveyance of political satire specifically through imagery (eg http://www.gutenberg.org/files/20759/20759-h/20759-h.htm).
Readbility uses background colour highlighting, keeps some formatting such as pulls and retains images.
You're welcome to prefer plaintext, some prefer black and white TV I'm sure, I just find it rather lacking in presenting the diverse types of information I wish to send and receive by email.
And just to note, Readability actually preserves bold, headings, breaks, and italics, while providing a different set of fonts and colors based on the user's preferences.
I see what you are saying, and I partly agree, but I am of the opinion that language is rich enough to emphasize relevant points without further aids. But it's becoming SO common to use _SO_ many aids that this is already standarized with two levels in HTML, namely the em and strong tags. How long until we need a third semantic level of emphasis? Of course, I enjoy freedom and choice, so assume people/the market must prefer your style by and large.
For the record, I know that italics typography has been used for centuries as an aid in emphasis. Still, I humbly feel this is an unnecessary artefact, which more often than not turns into a crutch.
Buttons for clothing have been invented, pretending that my coat doesn't need buttons and then holding it together with my arms so I don't freeze doesn't make sense to me.
Aweber and Mailchimp, for example, provide the basics needed for sending HTML plus plain text emails.
Sorry, I haven't been able to load the site in this post as it's not loading, so I can't comment on any specifics.