Other cultures would have vastly skewed results: for instance, my girlfriend is Qatari, her interaction with males outside her family is very strictly limited, and vice-versa for the males. Segregation between genders is enormous in some cultures.
This study is about same-sex friendship preferences, so the frequency of interaction with members of the opposite sex in these cultures is not the most relevant.
That being said, I agree with the person you are replying to. Differences in friendship preferences by men and women could be highly variable in different cultures, so one shouldn't read too much into a study that looks exclusively at US participants.
In my opinion a multi-center study is needed. I believe other parts of the world have different values in friendships.
I agree with you. My best friend was poor (not anymore, he is a MD now) and had nothing.