Note that a rejected applicant will have learned from the failed YC interview and adjust his presentation accordingly when applying to another incubator.

Kudos for your postmortem optimization feedback loop. This is one of the non visible features of YC that could explain the difference. Do you record the presentations for later review in such case ?

For the applicants, this gives the hint that they should apply to many different incubators and angels before applying to YC so that they can learn from their rejection how to optimize their submission. ;)