As a Brit living in Ireland, I have been fascinated by the difference in the subject matter of the two traditions and how it illustrates the history and social background of the two countries (probably the most important function of traditional song).
Apart from love songs, which appear to dominate all traditions, the two most prominent subjects in Ireland (for obvious reasons) are emigration and politics.
When there were a lot of older singers around to record here, we used to wince "Oh no, not another bloody emigration dirge". This was until we realised that there isn't a family here which hasn't been affected by emigration.
We saw a number of people at our local dancing/song/music venue, around this time of the year, reduced to tears when an old musician/singer sang the emigration song, The Christmas Letter, and a description from the thirties, of an elderly farmer tottering up the railway tracks after the train carrying his eldest son on the start of his journey to America, produced the same reaction from us.
Jim Carroll