That's my point. If a VC can't even be bothered to look through or respond to opportunites that show up on their doorstep, how exactly can they be in a position to find or help startups? There wasn't even anything in the article about helping or working with startups. It's ONLY about getting the foot in the door and just letting YC do the filtering.
I think you're missing the point entirely. Yes, there's a chance that one of the people who cold emails them is good - but really, what are the odds?
With introductions, the referrer stakes his or her reputation on the referee. Make too many bad recommendations, and that cuts out a bad lead. The most successful organizations I know recruit through internal contacts - and it just makes sense from a VC's perspective to do the same.
It's about the best allocation of time vs good finds, rather than just finding every good opportunity.