Saying "we were wrong" is an apology in my book. I don't know what you want, but this is sufficient for me. If you think your reading experience would be improved by grovelling, find the publication that grovels or has never ever made a mistake and read that. But for me, I'm ok with the Economist.
> If they didn't add that you would get a stream of people
A stream of people where? Only subscribers read this. Folks who have issues like you do wouldn't be subscribers to begin with. If they hadn't printed the mea culpa, few would have noticed.