As others have pointed out, YC (and VCs in general) have definitely expanded outside of pure software companies and a number of them have done well (see Dollar Shave Club). I think it remains very hard to classify companies as lacking in huge potential from the start—originally, I was very skeptical that DSC would ever be worth a billion.
I suspect that it's still a requirement for YC founders to be interested in aggressive growth. It's still for startups after all—I don't think anyone would get in if they admitted their sole goal was to reach <$1m/yr in profit.