There are very few billionaire charity projects that don't have some kind of bait stench associated with them...
This site is a lot less brazen that, say the Gates Foundation or Jack Dorseys "all the strings attached" charity "donations", but there's no doubt it's run in the interests of YC and they're doing it for the benefits they get.
Not that I begrudge them that. It just needs to be something you bear in mind when wondering about odd looking article rankings or apparent voting/submission patterns that evade the fraud detection... It's their space, they can do that if they want. I (and everyone else) needs to weight up the benefit to themselves against the benefit to the people in control, and determine whether to hang around here, or walk away. For me? They do an OK job of not taking too m much advantage of their ultimate power here. I'm mostly cool with them.