This used to be the "solution" to spammy links: Drop their value to zero. This caused an entire eco-system of spammers with the mentality: "I'll just generate 1000 links without the prospect of a penalty in the hope that 10 links stick. I then bill my client for a 1000 links, since there is no way to see which links are devalued".

Google's creative solution was to make sure to webmasters that: yes, these links do hurt your rankings. Instead of linkbuilding and diluting the precious link-signal, these spammers now offered link-profile-cleaning services (Mission. F-cking. Accomplished. http://xkcd.com/810/ ).