I was primarily responding to the comment that they were not separate industries, and supplying an example of similar marks that were not actually trademarked by Rackspace and thus open to potential use even by those in the technology industry.

Legally, technology and conferences are entirely separate industries with very different business, legal, and tax considerations. A technology company that makes software for conferences is not in the conference industry; a conference with technology subject matter is not in any of the technology industries. This may be splitting hairs, but the law is always a matter of splitting hairs.