 :Sure.  As a term, the list may be more common now than the radio format.  I was just tired of putting top 40 in articles and having it come up red.  I do think the radio format was first though.  Having 40 songs in rotation is just about the right number.  I remember some Top 30 stations and they just didn't make it.  Too repetitive even for pop radio.   On the other hand, I noticed the same thing about the links that you did, and stopped making them.  I can't quite imagine the content of the US Top 40 and UK Top 40 articles.  I suppose they could be lists of annual top 40 lists.   The radio format is important for noting all the wack songs that have made it.  The Mormon Tabernacle Choir is not what you usually think of as a Top 40 group, but because of the radio rules, there it was, mixing it up with the pop bands.  