Snowden in particular did much dumber things than using PGP: he used Lavabit, a "secure email provider" with an architecture any expert could have told you from 10 miles away to avoid, and some amount of the Snowden/Poitras/Greenwald coordination occurred over CryptoCat, which was grievously broken in several different ways --- it is almost certain that every message exchanged between those parties on CryptoCat has been recovered by SIGINT agencies.
People wonder why crypto engineers on message boards are so shrill about this stuff. This is why.