This is called pronoun dropping [1] and happens in quite a few languages, including Japanese as noted.
I had a friend in college who would always point it out (in English, where it's not very common). I still notice it often years later and I'm pretty sure it's thanks to her making me aware of it.
Interesting. The Chinese examples on the wiki page sounded completely natural to me and are in accordance with how I speak/interpret the language, but I never realized I was dropping pronouns due to their inference.
