Of course the market is saturated. But I do not think these sites will hurt the profession. If these sites were what the doctor ordered why are there folks like Jody Dole who seem to have no problem getting photos. There are editors out there who are willing to pay for what they want. If they want something generic they go to the buttloadophotos.com or genericphoto.com type of places and pick it up cheap. If they need a specific shot that can only be achieved by a specific photographer then that is where they go look.
Maybe the market will be harder to break into if these are the types of shots you are taking but elbow grease and paying your dues does pay off. Of course being a damn good photog with an original eye helps a hell of a lot.