A friend of mine (from another forum) who owns many NFA items, sent me this link today. It's a somewhat lengthy read regarding some history of the NFA, but I found it very interesting. If you have the time, I'd recommend reading it.
If you don't have the time, and want just the Cliff Notes, basically the author couldn't find a reason for suppressors to be in the NFA either. Also from this research, its seems the whole NFA was enacted just to combat Al Capone and other gangsters of the era. The $200 figure (tax stamp) was derived as a 100% tax on the price of a machine gun at that time, which has never been changed.
If you don't have the time, and want just the Cliff Notes, basically the author couldn't find a reason for suppressors to be in the NFA either. Also from this research, its seems the whole NFA was enacted just to combat Al Capone and other gangsters of the era. The $200 figure (tax stamp) was derived as a 100% tax on the price of a machine gun at that time, which has never been changed.