They're not common law as in if you were to try and hold a common law court there it wouldn't be recognised. Common law court is only recognised in the US and the British commonwealth, if you know how to to it. It's what Karl Lentz deals in if you've heard of him? He, however, is more of a believer in the system and chooses to play the games.
However, I agree with what you're saying. These are all constructs by people and exist if we believe they exist. The true definition of common law or the law of man may vary individually, but for me it is our respect of other people and not harming them or interfering with their freedom. These different laws are effectively games and rituals, but it's so widely believed that it's hard not to get caught up in them.