It's true, of course, as you'll see below, that income increases with every increment of education: A high school graduate earns more than someone who didn't graduate from high school; a person with a bachelor's degree earns more than someone with a high school diploma; and someone with a master's degree earns more than someone with just a bachelor's. (This is not true for every person, of course, just for groups on average; Bill Gates, whom I'm pretty sure earns more than yours truly with a Master's Degree, never finished college.)
But it's wrong to say that graduating from college is the cause of the income difference. It's true that earning a degree opens new doors to you, and new opportunities for income, but some of that can be explained by the fact that the best students in high school--the ones who are probably likely to earn the most later in life--are also the same ones who go to college. In other words, the same factors that get you into college are the ones that increase your chances for success.
Still, this visualization tells an interesting story, in four views, via the tabs across the top: On the first view, you can choose your own comparison: Use the filters at the top to select the values for the blue bars and the orange dots, to see the gap between any two education levels. You can choose men or women, and you can pick inflation-adjusted dollars or nominal dollars.
The second view, Income by Attainment, you see the whole world laid our for you. Pretty simple, and again, you have some choices to make.
The third view is where it gets really interesting, and where you see the disparity between men and women. This (and all the views) show workers over 25, so some older women may be skewing this, but it's still telling. And shameful.
Finally, the last view shows how much each step up gains you in income over the last one. A couple points are annotated for demonstration purposes.
As always, don't just look at these: Interact and explore the data. And let me know what you find.