Not true. Discovery subpoenas are well-established legal instruments; the term 'subpoena' just means 'under penalty,' in other words it carries the authority of the court or issuing agency to impose punishment for non-compliance with the terms. See for example http://www.weil.com/files/Publication/9f7ab3cd-f7d4-4eb5-b98...

The term 'discovery' has a specific legal meaning, and I'm not sure if that was what you actually meant.