It's an easy way to find common ground for casual conversation. Same goes for sport, mention the latest $popular_sport_match and you're bound to find that at least a few people will have seen it, or heard enough about it to make conversation.

For some sports it's even an international thing. I don't really follow rugby, but when I was recently in Fiji, I spent a fair bit of time talking about rugby and the Lions tour that was on at the time, because it was something that I could talk about with most British and South African people. Obviously, you can't go to another country and talk about the Red Sox, but for international sports, it's a great conversation starter.

Same goes for things TV shows like Game of Thrones, everyone watches GoT.

It's the same with the weather, it's an absolutely banal topic, but it's a common ground, we are all experiencing the weather.