I will grant that many people want rich text, formatted emails with images and logos. I don't want that but understand the wants and needs are different for others.
For gods sake why HTML? A fairly simple markup language (Markdown, orgmode, etc) would have sufficed, would have eliminated the need for separate plain and html versions of every email, been far more accessible to screen-readers and other assistive devices, been far less privacy-invading, and been far less vulerable to security problems.
But no, the answer was "let's put a full-blown web browser in every email client"
I know the horses have left the gate.