No, bloggers do not “have to make his links Nofollow”, but they should definitely moderate their comments and delete all spam comments.
There doesn’t seem to be anything new here. Google has held the webmaster responsible for all outgoing links on his website for many years. This is just a restatement of their long-standing policies regarding outbound links.
What seems to be the positive, yet unspoken conclusion you could draw from this is that do follow blogs, that have heavy moderation of comments, can be valuable as backlinks. These types of blogs only allow highly useful comments to be published and those few comments that do pass the grade will be quite useful in a backlink campaign. I especially like those that close comments after a short period of time.
While nofollow comments can be quite useful for traffic when done properly, they will be worth little on a blog that doesn’t heavily moderate comments. The bottom line seems to be linked from quality blogs are worth more and wide open blogs, do follow or no follow, aren’t worth much if anything at all.
Spammers seem to be constantly searching for those wide-open sites to post their spam and Google is also looking for them to devalue those links. That’s why you must constantly and continuously build backlinks if you choose the path of the spammer, and you don’t if you choose the path of high-quality backlinks.
If you build your backlinks on a foundation of sand (spam) they don’t last and you have to constantly rebuild. When you build your backlinks on solid rock (high quality) they last and last.