Consistency

A friend of mine who works in advertising told me a story about consistency. He missed an error in a piece of copy that went out in an e-mail. The copy was slated to be reproduced in a variety of forms across a number of web sites and e-mails. Instead of fixing the error in the reproductions he and the rest of the account team decided that the mistake should stay, feeling consistency to be more important than correctness. Let me add that the mistake was barely noticeable. I think it was an extra space around em-dashes, or something like that.

Now in chapter 4 the book states, "Sometimes, consistency rules." I guess I'd like your take on qualifying the "sometimes" in that sentence. In my friends story the break in consistency would have likely drawn more attention than the error he missed. But readers might accept more egregious errors if they kept consistently reappearing. Do you have any examples that might serve as a guide? How are decisions like the one in my example reached at publications?

DK