Apparently, Robert Siegel did a segment on 'All Things Considered' last Friday on different municipal recycling programs in the DC area. His goal was to understand why the recycling guidelines are different wherever you go.
Some towns only take some kinds of plastic, others take everything but want you to divide out your paper from everything else. This piece does a good job of explaining how it's all driven by economics. There is not enough demand for products made from some types of recycled plastics, so it can only be feasible for a fraction of municipalities to recycle the higher number plastics. Also, it is more expensive or the city to separate things, but requiring citizens to do more means less will get recycled (people are lazy) and the city has to pay more to get rid of trash.