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.