OPRAH WINFREY is reported to have earned $98million over a period of two years, which figures out to about $1 million a week, or $200,000 a day.Talk is not cheap. But neither is it scarce. Talking heads of one variety or another are filling the TV screen morning, afternoon, and far into the night. A casual survey reveals over 25 talk shows, more than one for every hour of the day.The switching of networks by David Letterman, plus the entrance of Conan O'Brien and Chevy Chase onto the late-night scene, have made headlines usually reserved for truly earthshaking events. Everybody, it seems, is talking about talk shows. Why are they growing, with seven new ones this season? What is their special appeal? Who makes up the audience?The distinction between, say, Geraldo Rivera and Jay Leno is too vast to permit simple generalizations. But certain themes occur and reoccur: 1. Few talk shows abstain from gossip. Talk show hosts from Johnny Carson on seem to have taken post-graduate courses in innuendo, applied, as the news of the day dictates, to Elizabeth Taylor, Michael Jackson, or Princess Di. 2. High-decibel confrontation is regarded as the stuff a hit talk show is made of. Any host who can provoke Cher to walk off in the middle of an interview stands to gain instant fame. When guests are discussing two sides of a controversy, the nearer they come to blows, so the conventional wisdom goes, the higher the ratings. 3. Confessions are the heart of daytime talk shows in particular. The host (or hostess) will sob along with guests, and presumably the audience, as the most shocking secrets are shared with millions of strangers.In short, talk shows are less info than entertainment. But wait. Doesn't Al Gore appear on Phil Donahue as well as mud wrestlers and exotic dancers? Don't issues - real issues - get aired in the midst of all the dirty linen?True. Still, there is something intrinsically trivializing about talk shows. Even the questions they raise about themselves tend to be more titillation than substance. Is Dave more hip than Jay? What niche is left for Conan or Chevy? Will Arsenio Hall survive the shakeup? These are the hot questions of the moment and have even led to a talk show talking about all the other talk shows. Stay tuned - with your "mute" button at the ready.