The article explains why the VC doesn't want to give the referral, but it doesn't explain how it can hurt me to ask. If you have ever sold something, you know, you have to ask a lot of unlikely people for help before you get any.
I can see this from both sides. We are trained as entrepreneurs to ask, ask, ask. If they say no, ask them who might say yes. But if they say no because they're a biotech late-stage VC, and you're after social-web angel funding, so they read your first two sentences and then turned off - what value does a referral really have?
It all comes down to doing your homework, IMO. If someone who should be interested declines, they can probably help you. If you're mass mailing every VC in Silicon Valley and asking for introductions from those who bother to reply to your poorly-targeted pitch, well, you've got a bigger problem than a VC writing a blog post about you.
Rejection's just a matter of business, but if he refuses to refer you and doesn't have a good reason (e.g. "everyone in my network is interested in biotech, and you're a web startup") he already thinks you're a loser and beneath consideration. At this point, getting his panties in a jam by asking a question he'll find annoying is a (small) benefit.
I don't suppose that this effect is large, but it might be noticeable.
Don't think anyone would poison a referral? If someone wasn't impressed by you, they might agree to the referral anyway -- perhaps thinking they are being nice -- but when they tell the third party about you, they say "yeah, this guy didn't impress me, but I promised him I would refer him to you."