The problem is... They are trying to place you at a job and taking a commission by obfuscating the actual salary paid by the company. I've personally hired developers, salaried under big recruiting firms, who were getting shorted 35% of their potential income just for allowing someone with a marketing degree forward over a resume. With demand as high as it is for skill sets in the tech fields... you are foolish to believe they serve any purpose other than spam. Especially when spending an hour or so shotgun emailing your resume personally with a cover letter would net you nearly double the salary.
Alas the core issue in this blog post has nothing to do with the abundance of recruiter contact. Anyone with a Linkedin has already managed to figure out how to manage the difference between spam recruiters and the good guys.