I do care, this shows that Mark is following G+ moves, wich also can indicate that Mark is acknowledging the fact that G+ is a direct competitor to FB. and also, You can prove it yourself :
1) Add Mark to a circle.
2) You will see him popup in the list of people in your circles who have played the game
The only thing this indicates is that Mark is keeping tabs on the latest hot news. It means that when a reporter asks him the question "Do you think G+ is a competitor to Facebook?" then he can give answer. The answer could be a simple no, but unless he's actually used G+ how could he honestly answer that question?
But you also need to prove that the Mark Zuckerberg account on G+ is THE Mark Zuckerberg.