The argument could be made that a company that provides free web-search services should stay out of the commemoration business altogether. No Olympics, no Christmas, no Earth Day, no Alan Turing's birthday -- nothing at all.
In any event, given that Google hasn't opted for 100% disinterestedness, the issue is not so much what it chooses to put in its banners. It's the difference between what it chooses to display and what it chooses to omit.