Cool as Freddy was, let's not forget these are ads for google - would he have wanted his image used to shill for a giant corporation?
I will agree that there is some commercial benefit to Google for this sort of thing, but even I'm not cynical enough to think that's their rationale for doing this.
Freddie Mercury was one of my biggest heroes growing up, and I thought this was really nice (and maybe will cause a whole bunch of young people to ask "Who the hell is Freddie Mercury?").