"It seems to me that, if you wish to interpret a song and make it your own, you sing it in your own accent - otherwise, you are just aping the person you heard

Good point Jim, and I agree completely. Unfortunately, I think that many singers actually wish to do precisely that - maybe not so much in the field of folk-music (although it does happen), but definitely in other genres.

Having said that, I personally try hard to sing in my 'Yellowbelly' accent but, if I sing a song I learned from, say, a recording of James Keelaghan, I find odd 'Canadian-sounding' words creeping in, and I have to concentrate very hard to avoid them.