Salient point about listening/reading their response, another tool in the social/life tool belt.
Re: weather, its not really about that, it's just opening the door that more often than not leads to a pleasant, random conversation with a total stranger.
I believe the significance or relevance of the "weather topic" depends on location. There are some places where the weather never really changes, and is indeed unremarkable, like southern California. But some regions can have drastic changes in weather, and some places the weather can kill. For example in the midwest US the weather can go from blizzard conditions to sunny and warm in 24 hours or a strong storm can destroy crops and ruin livelyhoods for thousands of farms. In tornado alley a "pop up" severe thunderstorm can throw off tornadoes and level towns. As someone who's lost family members to tornadoes, the weather is a topic I'm interested in.
Re: weather, its not really about that, it's just opening the door that more often than not leads to a pleasant, random conversation with a total stranger.