Its only a tiny, tiny minority of the population who are really wealthy.
The world's millionaires wouldn't even fill a small city (~1 million people), and the billionaires would fit in a large lecture hall / theatre / convention centre (~ 1500 people). In more poor/developing countries, you get the pyramid,
In rich countries, you get a hybrid pyramid/barrel.
(see this example from my own country http://taxreview.treasury.gov.au/conten ... erA-40.gif )
It is a breakdown of wealth by 10% segments of the population.
About 40% of the population are relatively poor(<0.5 of the average), 40% would be middle class (0.5 to 1.5 times average), and 10% are off-the-charts(almost 4.5 + times the average)
The reason for a perceived 'hourglass' is an imbalance in media reporting - we currently hear a lot more about the rich people and the nouveau poor. If anything, distribution of wealth in developed countries was a barrel shape, and appears to be moving toward a pyramid with a very pointy 'top'.
IMO. Technology is neutral in this shift. The main reason for the loss of middle-class jobs is that most of the gains in productivity, and inflated 'benefits' from the oversupply of labour are being re-invested into non-productive capital. This mostly takes the form of institutionalised exclusion from what was previously common property (e.g. the conversion of public spaces into private/semi-private property), and speculation (gambling on the future value of pieces of paper).
There has also been a recent change in the operation of most 'first-world' governments, where far more support is provided to the richest segment of the population for a much lower cost (i.e. taxes), while much less is provided to the population at large.