I have heard Casey quote articles from Rolling Stone magazine any number of times. Creem, Rock, and even the New Music Express from the UK, too. But I've never heard him quote an article or song/album review from Billboard. Only chart data.
Does anyone else find that a bit weird, considering Billboard and AT40 had such a close working relationship?
Just speculation on my part, but it may be possible that he quoted only from publications that had a broader public circulation, where more articles of a biographical nature were highlighted.
One other possibility is to show that the AT40 staff used multiple sources to gather their information for the show.