http://www.eere.energy.gov/consumer/your_home/electricity/index.cfm/mytopic=11020

The following extracts on rough numbers for small turbines:

AEO= 0.01328 D V

Where:
*    AEO = Annual energy output (kilowatt-hours [kWh]/year)
*    D = Rotor diameter, feet
*    V = Annual average wind speed, miles-per hour (mph), at your site

A general rule of thumb is to install a small wind turbine on a tower with the bottom of the rotor blades at least 30 feet (9 meters) above any obstacle that is within 300 feet (90 meters) of the tower.

Mounting small wind turbines on rooftops is not recommended. All wind turbines vibrate and transmit the vibration to the structure on which they are mounted. This vibration can lead to noise and structural problems with the building, and mounting on the rooftop can expose the turbine to excessive turbulence that can shorten its life.

Here is one that does make sense, from the Ontario Canada Gov't at this URL:

http://www.omafra.gov.on.ca/english/engineer/facts/03-047.htm

AEO = 1.64 D2 V3
Where:
AEO = Annual energy output, kWh/year
D = rotor diameter, meters
V = Annual average wind speed, m/s

So, in my case the avg. wind speed is 5 m/sec, and if we assume a 10m rotor diameter based on your example we get:
1.64 X 100 X 125 = 20,500 kwh /yr.

Ontario has just announced a fixed price buy offer for wind energy of $0.11 /kwh from independant generators, so at that rate we would expect to get $2,255 of electricity per year from the unit you saw.

This does not account for purchase or maintainance of the turbine, tower, inverter, etc...

It's about 2 households worth of electricity at current consumption rates.