In our PR agency, we find that it is true to say the top-tier guys rarely pick up news from a press release site, but it does happen sometimes (albeit rarely). For the top-tier we always send the release directly to the targeted journo/blogger/influencer and follow up.
We do get take up from mid-level blog and news sites from issuing releases via a wire service though (we like PRWeb and PR NewsWire - different services seem to work better in different territories) - those are a bonus and they usually give a link worth having.