Maybe you are misunderstanding what I as asking. Your saying there is suppose to be no difference between a html copy and a text? That makes no sense, they are not suppose to be the same or there would be no point. Such as a link with html it would be wrap with a href, in text it would not. HTML tags would just be shown in text and be sloppy? Almost all email allows you to edit both the HTML copy and Text copy that is send and you can see in the header 2 separate messages too.
Cut from Header
Content-Type: text/plain; charset=utf-8
text copy of mail
Content-Type: text/html; charset=utf-8
html copy of mail