For example running an online gamble site
If you are running an online site, you have to worry about which country your users are from as well.
There is a reason why some websites block US IP addresses.
There are still many cities in the European countries where gambling is illegal and some are planning to get it banned. It is limited to cities too while online gambling websites like poker were considered illegal sometime back. The laws for online gambling differs a lot from offline casinos and here in my country India, online gambling is also considered illegal and punishable but some websites have got a license like Rummy. Don't know what exactly is the law.
Even in India it all depends upon what laws specific states has. If you look at goa gambling is legal and you could find casinos over there.i am not sure about the rest of the regions.May be Rummy sites do take gaming license as there are no specific rule regarding that i guess.If at all if there is anything its not clear and i am sure there are loop holes in our law 