Usually deals are all about the capital/equity/valuation balance, right? Perhaps YC was able to make this a better deal for themselves and Quora by getting them

Usually deals are all about the capital/equity/valuation balance, right? Perhaps YC was able to make this a better deal for themselves and Quora by getting them to take part in a YC batch. The hypothesis may be that the other YC startups are so much more likely to succeed after being heavily exposed to an already quite successful startup.