It seems pretty counterproductive for Google to penalize the linked-to website for this, because they don't necessarily have any control over the links. This means that now a good strategy would be to make a bunch of spam links to your competitors' websites and have their rankings go down through no fault of their own. While that would be less effective than having your own go up, it's still useful.
What Google should do is make the links have no effect at all, thus preventing this abuse.
This is tricky. Generally the spammers are doing it because they're paid to do it by someone. Penalizing is the right thing to do. But you raise an interesting point - perhaps an unscrupulous firm would unleash a spambot pointing to their competition, to damage them. I'm not sure of a good way for Google to differentiate, other than your suggestion of ignoring.
Thank you for allowing me to talk myself into a circle. :-)
What Google should do is make the links have no effect at all, thus preventing this abuse.