Tipping culture varies from place to place and country to country. In the US, tipping is very popular and almost considered mandatory. And not only that, they are very, very high tippers (over 25% sometimes). In other countries, this is not the norm, to say the least. If you tip at all, it is a much smaller number, and it is not usually considered a requirement for each and every dinner or act of service.
If you are abroad and see someone tipping very high at a restaurant or a taxi driver, you can be safe to assume that they are most likely Americans.