It is also a question that is difficult to answer because a lot depends upon a lot on different variables, such as how old the couple are and how long they have been in their relationship. People who are in a new relationship tend to have sex far more often than other people (regardless of age).
Rather than concentrate on other people’s sex lives, it is much healthier to concentrate on your own, and work towards having a sex life that satisfies both you and your partner. What is the right amount of times to have sex for one couple may be completely abhorrent to another and so an average holds absolutely no value whatsoever.
This doesn’t necessarily mean being tied to the same person (controversial though that may sound) because not everyone is monogamous, but it should mean that you are not high handed with other people’s feelings.
Your question is usually the kind that is asked by someone who is not happy with their sex life because they feel that there is something lacking in their own; or by someone who thinks that they are a bit of a sexual athlete and wants others to know about it. Either situation is ridiculous: The second for obvious reasons, and the first because, if you are not happy, do something about it rather than make comparisons.