Not meant to be a criticism. If this was a normal "I'm sorry," a tweet or private message would have done the job. The very public dimension of this situation makes it a case requiring damage control, hence the multiple apologies on twitter, blog post, HN followup and so forth. It's a pretty good example of how to manage such a situation.
I also sent a private email to Heather apologizing. I felt a public apology was in order, as well, since the mean comment was done publicly.
Unfortunately, in such a loud, public setting as twitter, saying "I'm sorry" necessarily takes on a public form, as well.