Background:
RSS allowed syndication of links with metadata such as the headline that was associated with the link. Before RSS to syndicate links in real time, required screen scraping news websites to get the headlines.

After syndication became popular, ping servers were developed so that search engines could be prompted to index specific items as they were published. Before ping servers, you had to wait for a search engine to come along and index your site, which was no good for news.

Combining the two ideas allows for truly real-time search with minimum overhead.