What does "Executive heads have rolled down the network corridors" mean? what is tele-type?

"Nobody,” mumbled one astonished ad man, “ever assumed that viewership would go down.” Even now explanations abound. We are told the shows are even more miserable than in the past. That there is too much of this and not enough of that. Executive heads have rolled down the network corridors. We have been promised this or that new type of show. But the deeper truth is only beginning to emerge from the clouds of tele-hype.