This is just a way to find people who are already working and may be interested in changing jobs, but who do not want to post their resume to monster.com.
welcome to recruiting! :)
(except that a recruiter is totally unqualified to assess who can actually match their client's needs - even with their CV in front of them and the chance to talk with them by phone or in person)
That's why recruiters don't care about clients' "needs". They care about clients' "requirements"
"How would you rate your ability to harvest Karma from a site such as Hackernews, on a scale of 1 to 5?"
"eh, 3?"
"and reddit?"
"um, 5"
I promised to teach some stuff to some guys at work in a little study circle, then I guess it is finally time to brush up on my Javascript etc and send out the cv.
If they're unhappy, or need that extra $10k, let them go for it.
Or they can heavily encourage it, with vesting stock options, seniority based raises/promotions, etc.
Relying on "loyalty" to keep people when the employer has shown none (an employment contract that has penalties if you're laid off? Only for senior execs) is just a bad idea.