I've heard lots of stories about this issue, but I think you're the first person to actually have a statistically significant amount of data to back up what you're saying.
Can you elaborate on this point a bit? In particular, I'm wondering if it's the uneven stock split which is the problem, or if that and founder breakups are merely both symptoms of an underlying issue -- say, different levels of commitment from the founders, or unequal status levels.
Or put another way: If a team applies to YC and says that they plan on a 67/33 equity split, would you convincing them to change to a 50/50 split improve their chances of success, or are they still at a disadvantage compared to teams which originally planned on a 50/50 split?