How common is it that publishers withdraw a paper due to incorrect conclusions? Today there has been significant news coverage (at least in the UK) that the BMJ are withdrawing statements from two papers on the possible harmful side effects of statins. Here are the Guardian and BBC articles on it.

This led me to wonder how common such issues are in academia in general. In this case it appears the authors made an incorrect conclusion from a study which was not picked up in peer review. I can think of lots of similar possible situations where proofs may turn out to be incorrect or other data may be wrong/not properly dealt with.

In particular I'm thinking about less popular/controversial subjects where such things are unlikely to make the general news. Is it standard practice to issue a retraction if things are incorrect? If anyone has any numerical data on this that would be ideal.
COPE (Committee on Publication Ethics) have recommendations for what circumstances should lead to retraction of papers. Retraction is considered a very severe action and is not generally done lightly. In a document from COPE on retraction guidelines you can see what they recommend. 

Clearly that does not answer your question but the problem about being general in academia is that the effects of problems in written articles differ between fields. What is wrong is obviously wrong, but if the effects are risking lives  or is harmful in some other direct way will be more likely in some fields than in others. Hence retraction is probably far more likely in life sciences than in, say history or philosophy (feel free to disagree or add other better examples).