I think there's a cultural element to how much of it people will know to do without being explicitly told what to do.

In the US successful gatherings tend to require a fair bit of wrangling - I've been to more than one potluck where everyone showed up with roughly the same dish...

I think that goes everywhere though, I’ve been to at least one of every type of party described in this discussion thread in the last year and I’m not American.

MR. Quiche - we meet again..