This ties into annelyd's earlier annotation pretty well, and illustrates something I was hoping to expand on - declaring an annual day off is one thing, but unless the people get behind it, then it's just an annual day off. You need a lot of people who want to participate in order to create a full-blown holiday, and it looks like that willingness was there even before Congress signed MLK Jr day into law. Make no mistake, writing it into law definitely helped, but the sentiment was already there - all that D.C. did was to fence off that sentiment, so it would have room and time to grow into a tradition.