In the legal sense of "obstruction" (which is narrower than the colloquial sense) it's different. The law makes a distinction between refusing to help law enforcement, and actively hindering or deceiving law enforcement. It's not a crime to refuse to provide helpful information to law enforcement. The government can serve you with a subpoena for that information, but that's a civil process. While you can be held in civil contempt for refusing to comply with a subpoena, it's not a crime, and there are lots of circumstances under which people are "privileged" from having to comply with such subpoenas. (Lawyer-client, doctor-patient, between spouses, etc.) Journalists are generally held to be protected by a similar privilege.

Those privileges don't protect you from actively assisting in a cover-up or concealment of evidence of a crime, which is itself a crime. A lawyer doesn't have to tell a prosecutor where to find relevant evidence, but he can't help his client hide that evidence in the first place.