As with most issues within people, it is much easier to find blame than to ask those hard questions, like "why did my husband, or wife need to look outside our marriage for something he/she obviously wasn't finding within it?" Blame is easy - you shift cause to something outside of yourself when the real issue is in you. An affair is certainly a catalyst for self exploration
It's interesting to see the motivation of the 'other woman' or 'other man'. There is usually no malice toward the wife or husband being cheated on. The intention of having a sexual encounter with a married person is often without intention and is more a spontaneous liaison. Unfortunately once that liaison has started there are all sorts of reasons not to stop it.
Redressing the issue is for the married couple to be honest and open with their relationship and see what is lacking in it. It is a cop out, way way too easy to blame the other woman.