Jim, it's not just that people often post lyrics or videos online & credit the particular performer instead of the songwriter, but recently when I & a couple of others politely informed a YouTube poster of the identity of the songwriter (Bob Blue) when he had credited a performer of "The Ballad Of Erica Levine") as though the songs was original to her, he refused to change the attribution in the video description or title on the page. He argued with us, saying that it was customary and proper to credit the performer (recording artist, etc.)!

His argument was that when a song is principally associated with someone (e.g., Elvis Presley and "Blue Suede Shoes" or Frank Sinatra and "My Way") it's SOP to give the performer credit.   Of course, in many cases more than one artist has a hit with it (especially in different decades), and I don't think "The Ballad Of Erica Levine" was ever such a commercial hit for anyone that it's become indelibly linked with a performer's name.   But even in cases such as "My Way," which was a signature song for Sinatra but penned by the then 25-year-old Paul Anka, it's only fair and proper to give accurate authorship information.