Jeez, you'd think the American public had never seen a breast on television before. This site puts Janet's nipple in an historical context with a survey of nudity on broadcast TV from the 1950s to today.
Nudity on Television (TV Acres - thanks George)
See also: Nipplegate: The Index (Banterist, via Gawker); The Tit Shot Heard 'Round The World (Wonkette)