Recruiters are there because they are useful. Yes, not all recruiters are scum and low life bottom feeders that we love to hate.
To answer your question, systems are just systems. They can never replace the human element which is required when dealing with people. Hiring is a friggin tough job and I can totally see the value of "good" recruiters now that I have been looking to hire people even though I am too small to hire recruiters yet.
Good recruiters can do the initial "human" filtering of connecting the hiring team/manager with better candidates. Online Systems cannot yet do that. Most online systems can be rigged with Bullshit Resumes and there is no way to tell unless you talk to the candidate. Good recruiters can separate the wheat from chaff before it gets to the hiring manager.