Very true. However, the impression I've gotten from recruiters emailing me is that most of them are just sending uncustomized emails to a lot of people who match some keywords. If that is the case, then contacting 100 people instead of to 25 people means an extra hour of work. I don't think it's worth paying $5/contact to avoid something that takes so little time.
Conversely most e-mails from recruiters get ignored. I'd be far more likely to take an e-mail that I know someone had to pay to get to me seriously, on the assumption it'd likely be better targeted.
That might be an argument for premium job sites like TheLadders advertised as ($100k+ jobs). It seems like they've backed off on that branding, though. So maybe that doesn't work out well in practice?
