Democracy isn't just about government. It's a way for humans to organise in a shared space.
No, it is not. If you share an apartment you don't vote how much to pay to the landlord. You have a vote when you own a share or you have a consultative vote when the owner is interested in opinions, but other than the government nothing is a democracy. Even going with friends on a trip is not a democracy, it is either a consensus or there is no trip.
A flat isn't strictly a shared space though. It's a space your landlord owns completely and is renting out to you. HN is technically pg's/YC's but it's clearly been setup to be a reasonably fair facsimile of democracy, with a few obvious differences (people with more karma = more power) but upvotes and downvotes are definitely a democratic process here.