Rather than get into specific song discussions I'll just say many of the "two chord" songs listed above, depending on the artist, have three and four chords as written. Maybe we have thus discovered another avenue in what is "Traditional" & what is "Folk Music". For a long list of two chord songs give a listen to Cajun Folk Songs. Seventy or eighty years ago the German "button box" accordian was introduced to the Cajuns. The box is limited to two chords which changed the entire sound of Cajun music. As the box most often is in the key of "C" the Cajun fiddlers began to tune each of their strings down one note to allow ease of playing. The normal "D" string becomes "C". With a "C" box, "G" is the other chord. If an "F" is played by the fiddler the box has to fake it. A few Cajun tunes have three chords but the "feel" of the Cajun sound is lost as well as the "feel" of the French/Cajun classical beat. Zydico takes all this a bit beyond by instead using the Piano Accordian which can play in any key and allows standard three or more chord Rock & Roll tunes to be played with a pseudo Cajun flavor. Many Polka tunes German/Polish are also two chord songs. As mostly they are long dance tunes, to keep them from becoming mundane they are played alternately in two keys or four chords. Hint....Some fiddles take the above de-tuning quite well....some/most don't....so if any of you fiddlers have a fiddle with a sound you are dissatisfied with, tune it to a Cajun tuning and see if it improves. If it does it has much more value on the Cajun market. Sell it to a Cajun...buy the new one you have your heart set on....new life for an old fiddle.....everybody is happy.