The reason for the growing income disparity

Up until the mid-seventies productivity gains meant greater increases in income which makes sense given that more productivity means that more money exists to pay employees, and since those employees are making more many they are more valuable.

Yet now wages are no longer tied to the value a person brings to a company.

So what caused this to change?

1-An increase in the number of potential employees world wide began to grow faster than productivity gains, because while productivity tripled in Japan, China, Korea, Taiwan, Eastern Europe, and more recently countries such as Brazil, these countries also began to require more and more jobs. At the same time the number of people in the U.S. looking for jobs began to grow for a number of reasons.

Bottom Line is that the more people who are applying for the same job, the less any company has to offer to fill the job with a skilled employee. So skilled jobs will pay less.

2-Inflation wasn't reduced as it should have been. 

Normally the decrease in income and an increase in productivity would have meant that the cost of living should have decreased as it became cheaper to build products. However, while many things such as computers, food, and other similar items have all fallen drastically in price the cost of living has not decreased substantially. Why not?

Housing

The rapid increase in housing prices meant that people had to pay more for a place to live which increased inflation and prevent costs from dropping to some extent.

Part of our productivity gains are going 

to pay for more expensive housing.

Technology 

In the seventies the average household owned a single TV, the price of which was decreasing every year. However with VHS/DVD/Blueray, HDTV, Cell Phones, Computers, Internet, Cable and more the number of things each household spends it's money on grows to replace dropping prices of other items. This also means that those providing services and selling products have to charge more in order to get the things they want.

College

Increases in tuition prices have mushroomed out of control, which in turn means that those who graduated have less and less money.

Health Care
People are paying for things they never would have dreamed of which is putting more strain on nurses and doctors who also have to pay higher tuition costs, as well as other factors are pushing up the cost of health care which requires business owners to charge more for their products in order to afford the care they need.

3-CEO Pay 

CEO's and other executives have taken substantial pay increases during the time in which wages have remained stagnant for most people. However, this rapid increase in CEO isn't substantial given the size of the overall increase in the amount of money made.
Further Executive compensation began falling in the late 1990's but this changed nothing as far as median income growth is concerned. 

http://www.economist.com/blogs/graphicdetail/2012/05/ratio-ceo-worker-compensation

4-Regulations

Regulation costs have increased over 7% in just the last four years, they now account for over 1.75 Trillion dollars in cost to businesses. Which means that 1.75 trillion dollars has to be taken out of peoples pay checks to pay for regulations. If your curious that is about $11,000 per person who has a job in this country (US is currently employing about 150 million people) That means that the seven percent increase in regulation just cost you about $800 in pay. 

(Source for regulation costs Washington Times)

5-Gas and Resource Prices

More and more people want to buy a limited resources, so what happens? Yes prices go up, and that's exactly whats happening with gas and those increasing prices are decreasing your wages.

6-Government Debt

The increase in government debt has pushed up inflation a lot by decreasing the value of the money you own.

Solutions?

Now we come to the fun part of every problem, the solution.

1-Decrease regulations and create smarter regulations.

Dropping the cost of regulations by 30% would see an additional $3,300 per worker added directly to the economy. What's more it would allow more businesses to start up and stay in the United States.

2-Give shareholders greater control over Executive Pay in order to try to keep costs down.

3-The government needs to stop artificially finding ways to increase the cost of housing. Housing isn't a winner for everyone, those who don't own houses are trapped outside the system and even those who do become burdened with greater risk when these bubbles pop.

4-Decrease the cost of college and healthcare (Most all current plans being tried increase these costs)

5-Increase peoples options in job training so that its easier to learn how to become carpenters, a skilled manufacturer, etc.