I can see why they didn't use them. Launching your chem/bio weapon from an RPG means you're in range too.
It doesn't matter. You'll only read about this stuff in tabloids like the Post. The mainstream media will never put this on the front page. From the article: "Lt. Col. al-Dabbagh told London's Telegraph he was the source of the British government's claim..." It's originally from the London Telegraph, which, happily, is definitely not a tabloid.