While they may have good reasons for removing the original article–such as not wanting to risk someone missing the correction–such a removal always strikes me as “We did something stupid, now we’re trying to cover it up”. It’s great that they’ve taken responsibility and posted a correction, but, in the digital format, it doesn’t seem like it would be hard to correct the article itself. And they could add a “We regret the earlier error” at the end.
Call me nitpicky but I remember several years ago when Elsevier was caught deleting articles from some of its electronic archives. They had good reasons–some of the articles were plagiarized, for instance–but these were digital copies of the print publications, and there was no explanation why, when a patron would click on an article title in the table of contents, they’d get “404 not found”. It took a court order to stop them. It was a solemn reminder of how tempting it must be for some publishers to rewrite history.
