Practical Transparency
Forget silent data loss, even the SEC can't get basic RSS right. The feed Tim pointed to yesterday (financial filings) declares itself as RSS 2.0 but uses rdf:about instead of <guid>. But that's really beside the point. As someone pointed out in the comments, you want this information to be accepted and managed by a third party (e.g. a regulatory agency), not managed by the company itself, at least for the financial filings. How about for press releases and the like - not-regulatory filings, but still material data? For similar reasons, I don't think that simply publishing to the web is sufficient in itself. I can name at least one popular blogger who's been taken to task for modifying or deleting postings and has been accused of "rewriting history" for doing that. There's certainly the potential for that if a corporate weblog were the exclusive source for those releases. I do like the Atom over XMPP idea though. Pinging is becoming a tragedy of the commons situation. Pinging from certain hosting companies is reaching epidemic stage - some hosts will ping hundreds of systems for every new post on the system, regardless of whether that system cares about the content (i.e. has users who are subscribed). In addition, there's definitely evidence that the most avid fans of pinging are splogs; I see new posts describing for "pinging for SEOs" on a nearly daily basis. For very valuable information like financial information, a mutually agreed upon connection, like XMPP, is a much more optimal solution.