I am not a lawyer or cop so Caveat emptor:

I think that the vagueness in the law and probably case precedent is due to the tension between liberty and control. Officers want the be able to remove any threatening tool / weapon and individual at their discretion. OTOH, Americans feel justified in wanting to carry whatever tools / weapons they feel comfortable in using and our constitution, more or less, supports this. By having laws that make a statement towards control but are vague and interpretable, enforcers are free to be as controlling as they wish in most circumstances whilst allowing the illusion that there still is some liberty in our society.

Sorry if that brushed the edges of ranting <img src="images/graemlins/wink.gif" alt="" />