"So if you want a reasonable portion of users to see your email as intended, let's say 95%, you have to stick to the most basic features of HTML and CSS..."
There is no "need" to show logos and images, etc. etc. In fact, far from making things visually appealing, all of that tells me (and most other people) "this is an email which I can safely delete without reading", precisely because real people not trying to sell you something rarely do that.
> There is no "need" to show logos and images, etc.
…yes, there is. Email is a communication medium, and like in all written communication, an image can be useful. Do I really need to explain that images are useful in human communication?
I believe there is a human need for images, but also that only text is still capable of creating a lot more than you'd expect.
When email was monospace text, the whole ASCII art thing was glorious. People added ANSI escape codes and gave us e.g. the glowing, blinking Chernobyl cows, in plain email. I also remember seeing a giant ASCII art 'high-res' nude somewhere, intended to be printed on a matrix printer, on 5 or 6 pages of continuous paper (Long-legged she was.)
Writing this, I wonder what desperate marketing attention whores would produce with ASCII art.
Can you conceive your needs and your basic understanding of an issue is not, in fact, the whole thing?