I think about shows like White Collar, Mad Men and Damages. All amazing shows, well written, high concept, and somehow wrong for the major three networks.
There's no denying that cable networks are really leaps and bounds beyond the major networks with regard to taking chances with higher-concept material, although we've really reached the point now where the networks will occasionally reach beyond their comfort zone... but ONLY if someone else has been successful at it first. Take, for example, "Playboy Club" - NBC wouldn't have greenlit that show in a million years had a show like "Mad Men" not been a huge hit. In the end, though, it doesn't make them any less chicken-shit to really take chances, does it?
There are exceptions to the rule - "Lost" was one, although the chances of seeing another "Lost" on network TV anytime soon are pretty slim.
(Also, I should point out that I'm still terribly delighted we're getting another season of "Fringe", but that has less to do with an uncharacteristic lack of vision; Fox has always green-lit far more high-concept shows than the other 3 networks, it's just their nasty habit of cancelling them that has earned them a lousy rep. ;) )