One bit of software can talk to another, and all they need to agree about is the format of the data they want to exchange. What matters is that there's a format that can be understood on all operating systems. It doesn't matter. XML allows sites to easily establish an ongoing relationship with search engines. Each machine does what it's good at doing.
Network traffic is minimized.
The best picture of our site assembles itself on the search engine server. On our LAN it's easy and fast to find all the pages that changed. There's no need. We've been waiting for an agreed-to format for this functionality. I think every webmaster will recognize the value of maintaining this information.