I think Google need to completely devalue all blog comments from their algorithm and treat them a no-follow.
They know how to do this. The question is : why do they deliberately make it awkward and time-wasting for webmasters to have to write an email to individual splog owners (e.g. 1000 emails to send to 1000 individual splogs if you're a victim of a $5 blast that takes seconds for a script to do) and THEN sift through a spreadsheet of Google's "latest links" to carefully extract those blogs from all the inbound links and disavow them, being careful to put in your notes as to why those splog owners never did email you back (individually, for each splog). When Google make it SO onerous and difficult for webmasters - when they could have simply ignored such links they've ALREADY FLAGGED as spammy, you have to ask : why? For me, it's to cause uncertainty and doubt, with plenty of fear of course. Almost all webmasters these days view Google's organic SERPs with fear - especially if you rank well at the moment. Adwords are a more sure bet of course. The ONLY thing that will make Google change this policy is if it starts hurting their profits. If it doesn't, then they'll continue doing what they do, perhaps even dialling it up even more.