How many times does the google logo appear in various forms during the "tribute"? If you don't think google gains anything financially from this, then you don't understand how advertising works.
The Google Doodles have historically intertwined Google and whatever the day's message was. Just as in pre-interactive Doodle days where they would morph images into the Google name, here they are extending that into their new style of logos.
Plus, keep in mind that Google created the video. As a photographer and someone who enjoys art in general, I can tell you that it's not uncommon for artists to incorporate their name (or, in this case, their company's name) into a piece of work. It's a nice way to make the art something with which one can personally connect.
You are joking right? You think google inserts their logo into this video three or four times so they can "personally connect" with it? It is so when you watch it, you associate google with the "fun" feeling you are getting from watching the video.
I never said that was the entire reason, but if I were one of the artists involved (not that I'm any good with video), that would be part of my reason. When I take or edit a photo, although representing myself individually, I incorporate a part of me or my family in it–my name, somewhere, or sometimes even something that alludes to my company.
Now, I'm not saying that you are incorrect in what you perceive to be some of their reasoning for this. Of course Google wants to associate the work they do with their brand identity, and this video is indeed advertising. Anything a company does is advertising, to be fair.
That said, I don't personally believe that advertising and showing support for something are mutually exclusive. Just as a company is able to get their name out there while also donating to charity, Google is capable of spreading the Google name while also paying tribute to Freddie.
