I guess you're talking about the graph on the right. The bottom axis is quite clear, I guess, and the left axis is the population size, which seemed sufficiently clear to me for not mentioning it.
Not really -- for both graphs, a specific numeric value is given based on the mouse position, but not what information the graph is meant to convey.
Also, in a tablet, you can point at the chart with your finger and get the same information. Or, in this case, the lack of information. :)
EDIT: I just tried this chart on my tablet and you get the same data by pointing.