No, this isn't true, and this misconception is explicitly why I invoked the realtor problem. If the recruiter gets paid, say, 15%, the difference to the recruiter between $100K and $110K is $1500. To get $16,500 instead of $15,000, the recruiter risks extra days of negotiation in which the applicant may find another job, or one or both sides passing on each other because of lack of salary fit. In most cases, then, it is in the recruiter's best interest to pressure you to take the job at $100K. Most recruiters are out of the business in a couple years, only a few are in it for the long hall--since he's not going to work with you again, it's in his best interest to get the payout now. Over any length of time, they will make so much more money by you saying yes than you pushing for more money that it's stupid of them not to get you to take the first offer that comes down the pike.

A few recruiters, among them the best ones I've worked with, are in it for the long haul, and cultivate real relationships, but they are uncommon. I remain on good terms with them whenever I can--I've been on job interviews before where I was clearly sent to the wrong job and told the interviewer "look, you don't want me for this job and the recruiter just wasted your time and mine--go talk to this guy, he'll feed you candidates you can actually use." It's worth it, because what goes around comes around, but most are in-and-out and they act like it.