IMO, I don't necessarily think that the 9" or 10" dick is about satisfying the woman. I think it is more about strutting your shit, you know the cock of the walk so to speak. It's about a man stroking his ego (no pun intended) know that he has a big manhood between his legs and the next guy probably only has a 6" dick.
In his mind he thinks that the woman would choose his bigger manhood over the avg sized guy.
Of course this is coming from a guy that is..... well let's just say avg.