Advertisements from first run airings on Syfy is where the majority of the money comes from. There's just no justification for keeping a show on the air for the odds that someone in Sudan might watch someday.
Actually, it's a well known fact that most shows break even or loose money during the first run/network period, but make a profit by syndication and DVD sales. That's often why, if a show is close to the 100 episode mark but doing poorly, it might still get picked up to get as close to the 100 episode mark as it can for uture syndication.
And shows in native HD right now will have a bit of an edge as HD sydicated filler IS wanted by stations around the country.