Jane Singer found that almost none of the 20 US j-blogs she studied allowed users to post comments. Some regional or local newspaper blogs quoted and referred to their readers' feedback, but the big national media had almost no reader content. She also found that, although postings often had links (an average of 2.3 per post), the overwhelming majority were either to the host news organisation website or to a small number of elite news sites (Washington Post, NY Times, etc). Her conclusion: journalists 'are unwilling to relinquish or even share their gatekeeping role'.
I think she's right on the reason why. Most journalists doing blogs for their news organisations see blogging as a high-tech extension of their existing job rather than as something different. Columnists write blogs like their columns and reporters provide info, with links to the places they always get their news from.