It does say "It’s believed that with Penguin 4.0 Google has transitioned back to devaluing (or ignoring) spammy links, rather than penalising for them"
My working model is Google is working hard to make search relevant, as that's their bread and butter. If you do a Google search and you get spammy sites, you stop using Google, and they lose money.
Black hats will always be one step ahead, and will find very technical ways to beat Google in the short to medium term, and sometimes forever.
However negative seo is going to be such a common attack vector, especially against unsophisticated webmasters (which ironically might be the people with the most useful information, the people who Google DO want to show). So Google is going to consider this a major bug if such sites are getting attacked like this.
Ignoring but not penalising spammy links is the best thing for Google to do.