ISO standards are often discussed at PostgreSQL conferences, and whenever possible they try to follow the standards. Sometimes standards are written after PostgreSQL implements a feature, and it some cases it seems like they are even written to accomodate PostgreSQL (eg. the SQL/JSON standard seems to take into consideration that a database might have multiple JSON types just like PostgreSQL)

But whenever the topic of standards comes up, someone immediately mentions the high price of the standards, and I think only some of the developers actually have a copy of the SQL standards.