You're absolutely right, without ad revenue, those other verticals would probably stagnate. And Google needs all those verticals to feed into a central reposit

You're absolutely right, without ad revenue, those other verticals would probably stagnate. And Google needs all those verticals to feed into a central repository so Google can achieve it's ultimate goal of indexing and archiving all of the world's content. Search for the web, Gmail for our email, YouTube for our video, Google Voice for our voicemail, etc.