Another factor is greatly improved reporting. Rape in particular used to be very poorly reported, and this has improved a lot as the social stigma against reporting it lessened. The shape long rise from the 60s to 1990 was certainly strongly affected by that.
A number of reasons exist for the recent drop in very violent crime that the murder graph shows. Demographics are surprisingly only a small part of it. Most of it was the result of public health efforts that reduced the incidence of lead poisoning. See http://www.washingtonpost.com/wp-dyn/content/article/2007/07... for more. A much smaller factor which many have heard of was the legalization of abortion. While this has an effect, and was popularized in Freakonomics, the effect was much less than the benefit of reduced lead poisoning.