As a non-start-up person who'd really not likely ever do it but looks at graphs all day as a job, it does seem like the long tail makes sense, although it's hard to tell if 500 (plus a survey) is a representative sample. It seems like the usual thing for power distributions, you'll have a long tail with flying high salaries which is what most people think of when they think of founders (the architype of a walking hype and reality-disortion field emitting white man wearing a poloshirt), but you'll have a nice chunk near the bottom of the distribution which is "everyone else" who likely won't make a big exit. Don't the vast majority of start-ups fail? That description is the quintessential description of "success" for any variable with a power-law distribution.