This simply means there is no way the world can be divided into two or three equal parts without finding that people gambles regularly and almost everyone is involved one way or the other, from my research on gambling it has been existing right from Origin of man.
I don't think this is true, because at least in my family there are a lot of people who like sports and are not gambling at all. First of all there is a big difference between males and females being interested in gambling. From all the female friends I have and also wifes of my friends I know that there are only 1-2 woman who are really into gambling and like to bet, all the others would not use their money for gambling. Maybe in different countries there is a stronger mentality for woman to enjoy gambling, but also in the casino in my home town the male to female ratio is like at least 1 to 6, maybe even 1 to 10. And among my male friends there are some who don't like gambling at all, I think that around 60-75% of my friends enjoy gambling. That is why I would expect that maybe 30-40% of all adults are involved in gambling in some form. You also need to take into account that in some countries gambling is banned by the government which will lead only a few people doing it illegally.