"Back here in the UK, we're the ones supposed to have the ancient stupid laws not the 'Merkins."
Well you certainly have the ancient stupid joke.
It's not about the laws, nor the age of them, but about who gets to make them and which ones take precedence when Federal Law intersects State Law.
That is the biggest factor in why the US Civil War broke out. That is at the heart of the *legal* debate over "Women's right to abortion vs Right To Life" that undermines so many otherwise popular candidates at election time. That is what is being used as the stick for stirring the wasp nest in the Health Care debate right now.
And it is why you can gamble and pay for sex legally in some places in the US and will go to jail if you do it in others.
If the fact that it is America is blinding everyone you could just sub in "provincial law" for "state law" and use Canada as your text. I'll bet Australia has a similar system, but I can't say for sure.
The issue comes out of the lack of high speed coms and omnipresent law enforcement when laws were needed locally in a very large place. By the time centralization is a factor, no-one wants to give up what they've spent yonks getting working.
Why this is such a difficult principle to grasp is beyond me. I understood how it worked from watching American shows on telly long before I upped stakes and fled Thatcher's second term.