The NY Times has picked up on the impact that a weblog can have on an online retailer's sales.
The bottom line: it appears that the retailers in question have only figured out half the story and many are frightened of negatives, such as customer backlash or wanting to keep customers within the site.
Most run them "in hope of giving their stores more personality and giving customers a reason to return even when they're not in the mood to buy."
Partly right: weblogs remain a great way of interacting with a community (via the Internet) in a way which enhances an overall search engine strategy.