What was especially discrepant for me is that I have always remembered 1973 as a year when some of the best rock music of that era was released. With all this to choose from, it seems astonishing that the '70s station can't find anything better than Little Willy by which to remember 1973. But that's just the problem. Only then can it be uniquely associated in your mind with the time when it was first played. Good music from the '70s isn't particularly remembered as '70s music, any more than Handel's Messiah is remembered as '40s music.
Good music comes to be associated with the entire span of time during which it is played.
Some are still being played today. And because their currency extended beyond 1973, the '70s station can't use them as markers of that year. That's why the '70s station plays such bad music. In my case, it was junior high school. Steeler's Wheel 40's The 1740's, that is.