Now I am only going by that article, I haven’t read the book. But as it stands with the article, I am not sure I see how spammers are going to switch to RSS with any success at all.

Well, the article doesn’t say anything at all about spamming; it says that “web marketers” may turn from e-mail to RSS. Depending on how you define your terms, it may be the case that all spammers are web marketers; but it’s not the case that all web marketers are spammers. Their point may be that “legitimate” web marketers (however they think that term ought to be applied) are likely to get by spam filters and to have their messages go unread when customers are inundated with spam anyway, and so are more likely to move their means of communication to RSS feeds that users can voluntarily subscribe to (and unsubscribe from). Of course, some websites that specialize in advertising of employment or services that users have a significant incentive to seek out—e.g. Craiglist—already offer RSS feeds along these lines.

That’s my charitable guess at an interpretation, anyway.