You're right that accelerators are bound to fail, you're wrong to call YC an accelerator. That's what distinguishes YC, it's not an accelerator it's a company that funds lots of startups at once. Accelerator implies that you're going to artificially speed up growth, presumably in order to get the company an outside investment. YC doesn't accelerate growth and Sam in particular boasts (in a good way) about being a patient investor.
Also, don't underestimate HackerNews. How many other "accelerators" have a content hub that engages their customer base daily. You can't underestimate what that does for their brand.