To bring some statistics in: The Talent Code cites a study that shows that people who were famous enough to appear in the Encylopedia Brittanica in 1970 were disproportionately likely to have lost a parent at a young age.[1]
So there appears to be a correlation between losing a parent at an early age and extreme success. (That doesn't mean that your expected value is higher-it's more that the variance is greater.)
Eisenstadt went on a bit of extended speculation there.
Having parents tends to create a secure environment that leads to middling experience. Losing that doesn't make you work harder, it just takes away a "normal" life and leads you to find your way elsewhere -- either up or down (as SatvikVeri correctly observes.)
So there appears to be a correlation between losing a parent at an early age and extreme success. (That doesn't mean that your expected value is higher-it's more that the variance is greater.)
[1]: http://dheart.tumblr.com/post/305580832/orphans-rule-the-wor... (excerpt) or check The Talent Code chapter 5