The graph is visual, it's the relation visually; if you're trying to calculate the actual %change, then a table is needed. But having all the bars at full length makes it near impossible to see the differences between bars of length that are within a few % points.
I see the graph as answering the question: What is the difference in achievable wages between different "hacking" skills? The graph, as shown, displays that difference well. Like I said, there are no hard and fast rules, but I would have done it the same way!