YC continues to support my company nearly seven years after our batch, even though we're still tiny and have no plans to exit (and thus will likely never give them any financial return).
Sorry for not having mentioned this explicit (it is in my profile) but this is from first-hand experience from being a founder and having going through YC with Bitnami
I'm pretty sceptical that the phrase isn't a bit of marketing to some extent, but one thing (among many) that earns YC a ton of respect in my mind is YC Research. The research projects truly seem geared toward working for a better world as their first goal.