No matter where you apply Kelly as well as many other agencies do this. I worked for a major Corporation in CA and they use Agents as head hunters. When I was finally offered a regular position with the company I was surprised to learn that Volt whom I had been contracted through was receiving 35% on top of what I was being paid. Lets say I was not so happy thinking of how much money I had earned for this agency especially since I had been pulling regular 60+ hour weeks for more than 14 months. The agency claims its to cover benefits ... like what, they offer them IF YOU PAY for them. Going full time not only did I receive 35% more pay I received all paid benefits plus additional company benefits such as stock options, paid vacations etc. Volt does not have paid vacations but some other agencies do.
Unfortunately many companies now use these agencies to find their employees but read the fine print. Many times when you sign a contract they lock you in as a contractor for up to 2 years. This means while under contract you cannot apply or accept any permeant positions with the Company unless they buy you out from them. You cannot stay a contractor for more than 24 months (Federal Law) so many times you will be given a choice to a 90 day unpaid vacation or they usually just let you go. Kelly seems to be one of the better agencies but don't have much good to say about Volt. To Volt, you are a money maker for them and they could not care less about you as a person. The only time I ever heard from my agent was if I took time off (they lose pay when you don't work) and when it was time to renew the contracts.
Hope this information is helpful. Best of Luck.