(Reuters) - The Dallas Cowboys are the first North American sports franchise worth over $2 billion and remained the most valuable NFL team for a sixth consecutive year, according to an annual survey released by Forbes on Wednesday. The Cowboys have failed to make the National Football League (NFL) playoffs for two straight seasons but their value rose to $2.10 billion, a 14 percent jump from last year and nearly double the league average of $1.11 billion. The New England Patriots ($1.63 billion), Washington Redskins ($1.60 billion), Super Bowl champion New York Giants ($1. ... More...