Developers around the world have known for some time that search results can vary. Location has played a major role in filtering content that you search for. But the field has broadened to include other demographics, such as age, race, religious preference, type of computer, speed of your internet connection, and more.
Sometimes the differences between the opposite ends isn’t that great. Other times, it can be night and day. This adds to the growing list of things to consider when worrying about search engine optimization.