Why do so many American heroes begin with "J"?

Have you ever noticed how many male American movie heroes have names beginning with the letter "J"?

• Jack Bauer
• Jack Ryan
• Jack Reacher
• Jack Harper (Tom Cruise's character in the trailer that got this post started)
• Jack Slater
• John McClane
• John Kruger
• John Kimble
• John Matrix
• John Connor
• John Rambo
• John Spartan
• Judge Joseph Dredd (does that count as two?)
• James Bond (English character, American movies)

I'm sure the list could go on.

Is there some sort of rule I am not aware of?  To me this seems to imply that not every Tom, Dick and Harry can save the day - it's up to John, Jack, Joe and James.