doesn't that happen all the time though? whenever mudvayne covered king of pain i thought it was an original, until i learned otherwise. i know i can't be the only one who has heard a cover song and had no idea it was a cover. not only that but plenty of artists already don't sing their own songs, they may have tweaked a few things themselves but that would happen in this case as well. lines get stolen from songs, riffs taken from other songs, etc. one instance stands out is these are the days by the exies, but they didn't write the song another band did and only if you read the booklet notes would anyone know that. obviously only one instance in very very many booklets no one ever bothers to look through. just like all these taylor swift fans who think she writes all her own music, wake up.
i say again, a properly labeled cover song gives full credit to the original artist and does so candidly, not in the liner notes or in the lyric booklet. if it's not mentioned in the title or before playing the song, it's deceptive and shame on them. one such instance i can think of is one of my favorite folk singers, Iron & Wine. he gained a lot of attention for his cover of "Such Great Heights" by The Postal Service, and although it was a collaborative effort to have the cover included on the "Such Great Heights" single release, most people who hadn't heard of The Postal Service had no idea that it was a cover. transparency is important with this kind of thing, and i was disappointed that he wasn't more transparent about it.
that minor issue aside, there is a gaping moral difference between covering a song and purchasing a song from a songwriter, no matter how it's labeled or rationalized.