It could be that the rater re-evaluated and considered his previous rating still applied to the updated answer. (but it's quite likely that the rater is not aware of the correction).

I think some people just don't care, or perhaps they just aren't regular visitors to Answerbag. Active users check this site a couple times a day and receive email alerts when an answer is changed are much more likely to update a negative response. A casual user who happened to sign up one day, then rated an answer, but never gave it (or Answerbag) another thought isn't very likely to think about changing a rating. One other reason might be that the user who gave the neg. response was one of those people who come to Answerbag, read other people's responses, and LOVE to hand out bad ratings. They give them out sometimes for no apparent reason, other times over some insignificant detail. People like this aren't interested in making Answerbag a better site, they simply have more fun being negative than helpful.

To add to the existing answers, as we've seen on Answerbag lately, therer are people who rate answers with an eye to their particular religious morality, regardless whether the answer is correct or not.

It all depends on what you mean by an "incorrect answer". Answers may be rated down for any of dozens of reasons. Some answers are wrong. But then, so are some questions. Some people like to promote their own agenda. This does not mean their agenda is 'correct' or that it is shared by others. Some people plant questions, to invite a specific answer or to provoke controversy. They may then leap out with a great 'a-ha' if someone answers the question in a way they disapprove. That seems to be a popular pastime with some. Many questions are asked in an ambiguous fashion; not always for the person asking the question, but to the person providing an answer. Many users hold a specific sense of morality that others do not share. Does this mean their answer is wrong? Usually not, but some claim it does. I will toss out a simple example that may be of some use. If I pose the question: "Is infidelity illegal in Lutonia?", I am being very specific. The person answering the question will have a limited range of options: yes, no, or maybe. One could answer that: "Infidelity is not illegal in Lutonia today, but was for women up until 1703, as it was considered a danger to the line of inheritance to the throne." Nice clear question, nice clear answer. Now, for example, if I were to ask the question: "Is there anything wrong with infidelity?" Here we have a question with no clearly defined boundaries. What does it ask and what does it expect of the persons from whom an answer is requested? It does not specifically ask the legality of the issue. In fact, this is a very good example of a poor question. The person asking it could very well be asking whether or not the issue is strictly legal or asking what another's personal opinion is on the subject. Who knows? Sometimes those asking such questions rage against others, because they did not supply the answer the questioner expected or, perhaps, wanted to provoke. Sometimes they wanted the question to be somewhat fuzzy to provide them a soapbox for their 'grievances'. Perhaps they were trolling for personal satisfaction by trumping the opinions of others. If someone were to answer that infidelity is "Morally undefensible", that does not make the answer incorrect. It is quite correct within the scope of the question. The person asking such a question could say the person providing the answer was wrong, as there is nothing illegal about infidelity. True. But that was not what the question asked. If one wants a specific answer to a question, then one needs to ask the question in a clear and precise manner. Does this seem like nitpicking? Some might say yes, but it is within such very limited boundaries that such questions and answers become the defining articles of human rights in a court of law.