In FAQ: Does the rise of the LT = the fall of mass culture? Chris Anderson asks the question if the long tail - the increasing effectivity we can address niches with - means that mass culture will die.
Some personal perspectives: I'm from Norway, a country with a population of 4 million. When I was a kid (early 80's) we had three TV channels: The Norwegian public broadcasting service, and the then two Swedish public broadcasting channels. There were satellite and cable services but very few had them.
Everybody watched the same shows - I certainly do recognise that.
Fast forward to the mid 80's and we got cable. And so did the neighbours. And lots of my friends at school. Not many channels - 20 or so. But the transformation was still large. The public broadcaster was (and is) still hugely popular, but significant changes immediately occured in the viewing habits of many groups. Kids, for instance, were suddenly watching US and British cartoons, and teenagers started getting more of their musical input from Pat Sharp on Sky Channel rather than local DJ's (I still find it amuzing that a British channel was so vastly more popular outside the UK than in - most Brits don't seem to be aware of the old
20 years on and the landscape has shifted drastically. More media, more segmentation.
While I think there will always be room for some degree of mass culture, I agree that it's influence will drop - the curve will flatten. But it's human nature to want to belong to larger groups, to want to be popular and watch and listen to what others watch and listen to.
I think that the main change isn't that people doesn't want to find that any more, but that the sheer availability of media makes it incredibly much harder to cover the market effectively enough to build the kind of following you could easily get before.