Anyone who has seriously studied the history of American pop culture has to laugh at anyone who gives creedence to the Cowboys claim of "America's team".
This title implies only the employment of a savvy promotions director.
The Rolling Stones' tour director Sam Cutler first coined the phrase America's Greatest Rock n Roll Band in 1969. By the time this term was revised in 1975 people had gone from laughing at their self proclaimed title to acknowledging it.
The Cowboys of the 1970's employed the same tactics. They were the first to refer to themselves as "America's Team". After a few years the public forgot who first invented the term, and started using it as if it were factual.
Howard Stern performed a similar act in the mid nineties when he refered to himself as the "King of all media". The term was laughed at, but eventually was published without any challenge to the claim.
To sum up, the Cowboys are a popular, winning franchise. But for anyone who actually believes that they are "America's Team", I would like to point out that I am America's sexiest bachelor.