I don't like to jump on a bandwagon, but "aren't the ones you want clicking on your emails anyway. At least in tech." is a strange comment.
I want all the 15k employees and 65 k students here reading the information sent.
As there isn't a unified message board or client environment, a good email design is the only route to go.
And image based emails is not that route; I have shut off images for all my own mails, not for data or client limitations but because I want the information readable and not hidden.
And then we have the more important issue of text to speech. But that is a beast we have a department specializing in.
Late to this discussion, but it's a valid one.
Your points are very valid, and today most of our users read their work emails on the phone (I work at a uni).
There are a few more points I'd like to add, though:
5. As stated below, people with disabilities will have issues with images instead of properly designed text. And an email should be more about the textual content than fluff (in my opinion).
6. The amount of disk space it takes up. This may not be something we think that much about, but if an email is sent to 70'000 users the amount of physical space will be a lot different depending on if the mail is an image, or properly designed HTML.
7. A lot of ppl block images in their client (I do), because it's utterly annoying when you just want the quick lowdown on content.