In one of the games on Sunday there was a penalty against the defense and a dead ball unsportsmanlike also against the defense for taking off a helmet. The Refereee only penalized the live ball, stating "by rule only one penalty is enforced".

The announcer quickly picked up on the fact that if a live ball foul is called the offending team has a free shot at an unsportsmanlike foul. In federation all unsportsmanlike fouls are assessed.

Anyone know why the NFL rule is different?

They simply call fouls right after the play is over "continuing action" fouls and they can be used to create a multiple or double foul. That is just how they do it.

Just remember, plays can be fined for their actions so there's never anything as a freeshot.