No kidding. I've been hired through third party recruiters twice, and both times were fantastic. I am just guessing, but I got the distinct impression that both were doing better and were better compensated working independently (one owned his own business, the other was highly placed) than if they were recruiters for a large company.

OTOH, my experience with same-company recruiters was that they merely existed to act as a simple filter and PR person. They didn't invest anything in me (the candidate) nor really examine if I was a good fit before I got passed further on up the chain.

Now that I really think about it, the quoted advice is pretty much a mirror opposite to my experience.