First, for disciplinary purposes, the NFL views a punch and a kick the same way.
Second, neither a punch or a kick mandates an automatic ejection despite widespread belief that it does.
Third, the NFL fine system is based on a variety of factors, including previous offenses. Woodson, for example, received a $10,000 fine for his punch, which is a standard level for second offenses of unsportsmanlike conduct.
Given that context, it's understandable the NFL fined Minnesota Vikings defensive end Brian Robison $20,000 for kicking Green Bay Packers guard T.J. Lang in the groin last Sunday at the Metrodome. Like Woodson, Robison was penalized 15 yards in the game but not ejected.
I can't explain exactly how the NFL arrived at $20,000 for Robison, but it's possible he has received multiple fines during previous seasons. (Not all fines are publicized.) Regardless, Robison has already apologized for the incident and done everything he could do to move on from it.