Dublin Core is sometimes inserted into in the HTML header for search engine optimization purposes. I am very curious to know which search engine are being optimized for with the inclusion of DC metadata in the HTML header. Google clearly sates they don't use keywords anymore. Some argue that dublin core tags are different than keywords and therefore google might still be using them. As far as I know the specifics are a trade secret that Google hasn't made public. If anyone knows more on this please let me know in the comments.
I do know that Google's search engine scholar.google.com runs via a different bot and crawl process and does use some DC tags for identification. They have a sub-dialect of tags and have added some non-standard (not true dublin core) tags to what they expect. — how rude and presumptuous of Google... But Google Scholar is the only search engine I know about looking for Dublin Core metadata in HTML. If anyone knows of another one I'm very keen to know about it.
Bing sunset their academic/scholar service. My understanding is that when it was running, it was just one bot that crawled the data and then they filtered the single crawl to create the academic materials product this is a different approach than Google is taking.
Here are some interesting links on Dublin Core in the headers: