I get marketing emails all the time where the HTML part carries the message and the text/plain part... is last month's message. Or last year's. Or lorem ipsum.
I used to tell companies about this problem, but it turns out that of the thirty or so I contacted, only one was interested in fixing it. Now I just mark them as clueless.
I get emails where the text/html part is fully fleshed out, and then the text/plain part is just the string, "Can't see the formatting? Click here!" where the last two words presumably lead to an HTTP served version of the email text.
Hey, I can see the formatting. I just choose not to. If you, on the other hand, can't even attempt say what you want to say with plain text, it's probably not something I care about anyway...
I used to tell companies about this problem, but it turns out that of the thirty or so I contacted, only one was interested in fixing it. Now I just mark them as clueless.