Then there's the overall composition of the piece. The overall balance is similar although one biased to the right the other to the left, and the similar trait of something slanting into view at the left edge at about the same angle.
The subject matter doesn't even have to be the same in order to draw similarities. They just used those examples because they illustrate the point of the article the best. Had they tried to use more conceptual things like space or light it would have elicited even more "I don't see it" comments.