HN definitely has a topic, it's "things that hackers find interesting". Mainstream political news is usually off topic unless it's incredibly important. And you

HN definitely has a topic, it's "things that hackers find interesting". Mainstream political news is usually off topic unless it's incredibly important. And you definitely can't post about that pizza you had for lunch, unless it's a rundown of how you built an arduino-controlled pizza oven. Twitter has no topic at all. The interesting is jumbled with the inane, so the signal to noise ratio is very poor.