TV Show Longevity

Samuel Arbesman at Wired charted out the longevity of shows across TV history broken down by network, revealing, among other things, that "When one network has long-lived shows during a time period, such as ABC in the mid-1980s, another network might have a series of duds, such as NBC during the same time." I missed his chart from a few months ago trying to quantitatively determine "Golden Ages" of TV.